Any conversation about the Steelers' offense begins with Ben Roethlisberger, who was the team's first-round pick back in 2004, has been the starter ever since, and says he want to play another 2-3 seasons. And while Big Ben has a 135-63 career regular-season record and has helped Pittsburgh to three Super Bowls and two Lombardi Trophies, he's benefitted from some of the league's best playmakers on both sides of the ball.

When Roethlisberger came into the league, he had Hines Ward and Jerome Bettis. The names have changed -- Santonio Holmes, Willie Parker, Mike Wallace, Heath Miller and now Antonio Brown and Le'Veon Bell -- but the results have mostly remained unchanged. And we say mostly because the only two non-winning seasons in the Mike Tomlin era (back-to-back 8-8 campaigns in 2012 and 2013) were a direct result of fielding the league's worst defenses.

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The defense has steadily improved in the years since and the expectation, even without inside linebacker Ryan Shazier on the field in 2018, is that the Steelers can remain a top-10 unit (they ranked ninth in defensive efficiency a season ago, according to Football Outsiders' metrics). But for as good as the defense might be, in today's NFL, offenses win championships. And for the Steelers, that brings us back to Roethlisberger, Brown, Bell, the offensive line, and a handful of players no one, from the perspective of early May, is expecting to make much of an impact later this fall but whose ability to, in Tomlin's words, "be the next man up," could be the difference between making it back to the Super Bowl for the first time since the 2010 season and another in a recent string of playoff drubbings.

But despite the postseason disappointments, the Steelers' front office and coaching staff have had success at putting together a roster that wins a lot of football games. Again, having a franchise quarterback is a huge part of that but as we pointed out above, having a good defense and a couple big-play threats are damn near mandatory too. In fact, since 2004, Roethlisberger is second only to Tom Brady in wins (135 to 162), and ahead of Drew Brees and Eli Manning despite playing in fewer games (21 and 16, respectively).

And before you remind us that #QBwins is a terrible way to measure an individual quarterback's abilities, it does shed some light on how having a balanced team -- a franchise quarterback, offensive playmakers and a good defense, for example -- translates into sustained success.

But the Steelers are also a team in transition; yes, Big Ben reportedly said he wants to play three more seasons but two things:

1) Last offseason, he contemplated retirement; and

2) Here's what Roethlisberger said in January during a radio appearance about the "three more years" remark to teammates. I'm just playing it one year at a time. I'm excited to come back next year. 

"I know [Pittsburgh Post-Gazette reporter] Ed [Bouchette] said that he heard that some guys said something about me playing for another three years. I'm not going to look past one year. I'm going to look forward to next year and give it everything I have."

So here's what we know: Roethlisberger's playing in 2018. Beyond that there are no guarantees. And that reality explains why the Steelers traded up in Round 3 to take Oklahoma St. quarterback Mason Rudolph, whom the team considered a first-round talent.

"He was with the group of the top quarterbacks," general manager Kevin Colbert said during draft weekend, via PennLive.com. "That was a really good position. That's very unique to the draft. It usually doesn't come through with a nice group like that. ... We haven't had that much depth at the top of the draft at [quarterback] in a long time," Colbert said. "Mason was certainly a part of that group in our opinion."

Now the question becomes when will Rudolph see the field. His arrival almost certainly means that Joshua Dobbs, the team's 2017 fourth-rounder who didn't see the field as a rookie, will be the odd man out. And if Rudolph impresses in training camp and the preseason, he could conceivably replace Landry Jones as Roethlisberger's primary backup.

Beyond injuries paving the way to playing time in 2018, Rudolph's ETA under center could happen anytime between 2018-2020. The biggest problem, if you want to call it that: What if Big Ben continues to play at a high level and like Tom Brady, keeps coming back? That could mean that Rudolph, who will sign a four-year contract in the coming weeks, could be in the final year of his deal before the Steelers have any idea if he can play. But if the winning continues between now and then these are good problems to have.

What will a transfer of power look like when that day arrives? Let's take a look at the Steelers' 2018 offensive depth chart and what it could like like a year from now.

2018 Depth chart

QB: Ben Roethlisberger/Landry Jones/Mason Rudolph

We mentioned above that Rudolph could have a mind-blowing August and leap frog Jones on the depth chart but it's more likely that he'll be on the "learn by holding a clipboard" game plan for 2018. That said, Jones enters the final year of a two-year deal, and the Steelers could realistically be looking to replace a couple quarterbacks in a year's time if Jones isn't re-signed and should Big Ben retire.

RB: Le'Veon Bell/James Conner/Stevan Ridley/Fitzgerald Toussaint

One of the league's best running backs, Bell's versatility -- he had 1,291 rushing yards last season to go along with 85 receptions -- means he wants to be paid for his contributions beyond the running game. That's perfectly reasonable but a year after Bell reportedly turned down a five-year, $60 million deal, the Steelers have again used the franchise tag on him. And if the two sides can't agree on a long-term contract by July 15 -- NFL Network's Aditi Kinkhabwala said in April that Bell wants $17 million a year (that's Antonio Brown money) -- Bell will play the 2018 season on a one-year deal that will pay him $14.5 million. For some perspective, that would be a 75 percent increase over the $8.25 million average salary Devonta Freeman, the closest back, earns.

There's more: Bell has again threatened to hold out. A year ago, he skipped training camp and was rusty for the first few weeks of the season. And while the Steelers don't need Bell in peak form in September to help make their Super Bowl run, at $14.5 million, he should be. A year ago Pittsburgh drafted running back James Conner in the third round and he flashed in limited duty. His season ended after a Week 15 knee injury but on 32 carries he rushed for 144 yards (4.5 per carry). Expect him to get a heavier workload in 2018. The team also re-signed Ridley, a former Patriot who appeared in two games last season after Conner was hurt.

If the Steelers do end up franchising Bell it's reasonable to think that he won't be back in 2019. He'll be 27, coming off 406 touches in 2017 and however much work he gets in '18, and his asking price will have only gone up. And while Bell is a special talent, you can find comparable talent for a lot less money; remember, Bell was originally a second-round pick, and just last year both Alvin Kamara and Kareem Hunt were third-rounders. There was plenty of pre-draft speculation that the Steelers could take Derrius Guice with the No. 28 pick. It didn't happen, but with the future quarterback already on the roster, running back becomes a real need if Bell is entering his final season in Pittsburgh.

FB/H-back: Roosevelt Nix/Jaylen Samuels

Nix is a former college defensive lineman who went undrafted out of Kent State and eventually found his way to Pittsburgh where he was transitioned from linebacker to fullback. After signing a series of one-year deals, Nix inked a four-year contract extension in February weeks after appearing in his first Pro Bowl. He's core special teamer and a big part of the Steelers' running game, opening holes for Bell.

The Steelers drafted Samuels in the fifth round of the 2018 draft and while he did just about everything at N.C. State, Pittsburgh plans to use him, at least initially, as a running back. But his versatility -- especially coming out of the backfield -- is what makes him an intriguing third-down option.

"Kid is very talented, multi-purpose kid," Steelers running back coach James Saxon said last weekend. "He's done a lot of different jobs He's going to get every opportunity once he comes here to do a lot of different jobs."

And that will include special teams too.

WR: Antonio Brown/JuJu Smith-Schuster/James Washington/Justin Hunter

Brown is the NFL's best wide receiver and he's compensated as such. And even though he turns 30 in July, he'll likely remain atop his perch for at least two more seasons. The Steelers struck gold with their 2017 second-round pick, JuJu Smith-Schuster, who set the Steelers rookie record for receptions (his 58 catches were nine more than Santonio Holmes had in 2006) and will be an even bigger part of the offense in 2018. He's equal parts Hines Ward and Anquan Boldin -- and he's also fast, despite running a 4.54 at the combine (remember this). Here's a two-play sequence from December that exemplifies why Smith-Schuster is so good:

Any remaining skeptics should consult this play from Week 10 when Smith-Schuster outran 11 Colts to the end zone:

How good was Smith-Schuster's rookie campaign? He ranked sixth in total value among all wideouts, according to FO, and was first in value per play, 10 spots better than all-world teammate Antonio Brown. He was so good, in fact, that he replaced previous wunderkind Martavis Bryant as the No. 2 receiver. Bryant, who was suspended for the 2016 season, was traded to the Raiders during the draft and the Steelers promptly found his replacement when they took Oklahoma State's James Washington in the second round.

Washington, who put up ridiculous numbers in college (74 receptions, 1,549 yards, 13 touchdowns last season), also ran a 4.54 at the combine, which probably knocked him out of the first round. He benched 225 pounds 14 times (Smith-Schuster got 15), had a broad jump of 120 inches (same as Smith-Schuster) and a vertical of 34.5 inches (to 32.5).  Put another way: Don't let the 40 scare you; Washington's a long-armed deep threat who can make contested catches and he'll fit nicely into Pittsburgh's offense where he'll benefit from defenses focusing on Brown, Bell, Smith-Schuster and the tight end.

TE: Vance McDonald, Jesse James, Xavier Grimble

There were some mock drafts that had the Steelers taking a tight end, though that always seemed like a stretch because the team traded for McDonald just before the 2017 season and he didn't really appear comfortable in the offense until December. He appeared in just 10 regular-season games last season because of various injuries but when he was healthy down the stretch he immediately became one of Big Ben's favorite targets. 

We saw it in Week 14 against the Ravens, when McDonald flashed his athleticism and finished with four catches for 52 yards, including this swing pass in which he beat a defensive back to the corner for a 20-yard gain.

There was some question whether the Steelers would bring back McDonald and his $3.7 million base salary in 2018 after he managed just 14 receptions for 188 yards during the regular season. But he exploded for 10 catches for 112 yards in the playoff loss to the Jaguars and Colbert said earlier this offseason that he expects McDonald to benefit from a full offseason working with Big Ben. 

Jesse James is best known for The Catch That Wasn't in the Week 15 loss to the Patriots but he's a reliable blocking tight end who gives Roethlisberger a large target on short and intermediate routes. He doesn't have the dynamism or explosiveness of McDonald, but in this offense he doesn't need to.

Offensive line: Alejandro Villanueva (LT), Ramon Foster (LG), Maurkice Pouncey (C), David DeCastro (RG), Marcus Gilbert (RT); backups: Jerald Hawkins, B.J. Finney, Chukwuma Okorafor

A decade ago, the Steelers won a Super Bowl with one of the worst offensive lines in recent memory. The unit has been overhauled under Hall of Famer Mike Munchak and is regularly among the NFL's best units. But Pittsburgh lost one of its best backups, Chris Hubbard, to the Browns in free agency and they'll have to hope former fourth-round pick Jerald Hawkins fill Hubbard's shoes because it's unlikely that rookie third-rounder Chukwuma Okorafor will be ready to play in 2018. When healthy, this unit has kept Roethlisberger upright; he was sacked 21 times last season, 17 times in 2016 and 20 times in '15. By comparison, Big Ben was sacked 46 times during that '08 Super Bowl run and 50 times the following season.

So we have a pretty good idea what the 2018 depth chart will look like. But what about 2019? Because based on a number of decisions, the Steelers could be in full-on transition mode 12 months from now. 

2019 depth chart

QB: Mason Rudolph/Landry Jones/ draft pick or free-agent signing

Let's assume Roethlisberger retires. Landry's contract is up after the 2018 season so he may not be back. But the Steelers could sign him to another short-term deal, and even promise him a chance to win the starting job in 2019. Rudolph could get that same opportunity and the hope, obviously, would be that the second-year quarterback would win it outright. And then we'd get an idea if Rudolph was indeed a first-round talent or just another third-round quarterback that struggled to transition from a successful college career.

If Ben Ben returns in '19, Rudolph would likely be elevated to the No. 2 quarterback (assuming it doesn't happen this season) and the Steelers would need to sign a No. 3 quarterback.

RB: 2019 draft pick/James Conner/Jaylen Samuels

We mentioned it above: if the Steelers don't sign Bell to a long-term deal this offseason, he won't be in Pittsburgh in 2019. Conner is a solid back but he's not nearly as dynamic as Bell, which is why Pittsburgh could target a running back in the draft. Conner and Samuels together could approach Bell's versatility but not his playmaking abilities. 

WR: Antonio Brown/JuJu Smith-Schuster/James Washington/Justin Hunter

Brown's under contract until 2021, as are Smith-Schuster and Washington. Hunter, a former second-round pick, is on his second one-year deal. And while he's a rangy, fast deep threat, he'll need to play with a lot more consistency to get another contract next offseason. Either way, don't be surprise if the Steelers continue their annual habit of taking a playmaking wideout to add to the receivers corps. Whomever's under center next season will have the league's best pass catchers at their disposal. 

TE: Vance McDonald, Jesse James, Xavier Grimble/2019 draft pick

If McDonald plays as well as the Steelers expect he will, he'll be back in 2019, which will be the final year of his current deal.  James, meanwhile, is in the final year of his rookie deal though he could be back at a reasonable price. Grimble is on a one-year contract and it's not clear if he'll make the team in 2018; he's showed glimpses of promise but has never consistently put everything together. If a better option becomes available as the season approaches, the Steelers could look elsewhere. Expect the team to target an athletic tight end -- think Vance McDonald -- the the draft.

Offensive line: Alejandro Villanueva (LT), Ramon Foster (LG), Maurkice Pouncey (C), David DeCastro (RG), Marcus Gilbert (RT); backups: Jerald Hawkins, B.J. Finney, Chukwuma Okorafor/2019 draft picks or free-agent signings

Foster enters the final year of his current deal; Pouncey and Gilbert are on the books through 2019 and Pouncey's hinted that when Big Ben retires, he'll be right behind him; Villanueva is signed through 2020; and DeCastro's deal is through 2021.

As for the backups: Finney's contract expires after the 2018 season and Hawkins' after 2019. Okorafor will sign a four-year deal in the coming weeks.

The simple takeaway from all this: The Steelers' window is closing. Roethlisberger is the biggest, most important variable in all this, but a team stacked with playmakers and a worse-than-replacement-level offensive line is a team that will be lucky to go .500. But that's the game -- building a roster within the salary-cap restrictions and doing it better than the 31 other teams. The Steelers have a stellar record of finding players and winning football games, but if they don't bring home a seventh Lombardi Trophy next February, the 2019 season could be the official start to the rebuilding process. It only takes a few personnel decisions to not work out, a few untimely retirements, and a bad draft or two to set a franchise back three or four or five years. Pittsburgh hasn't had a losing season since 2003, a year before Roethlisberger arrived. One day soon the question will become: Have they done enough to prepare for life after Big Ben?