This isn't a question of whether Gronk will play. He'll likely find a way to be on the field. The real question is effectiveness, and based on everything I hear the chances of Gronkowski being a factor are almost non-existent. You don't recover from high ankle trauma this quickly and the fact he still hasn't practiced is the biggest indicator of the seriousness of the injury.
My guess is Belichick will try and use Gronkowski as a decoy. Put him in the game, run a few routes maybe, use him as a blocker if possible. But the idea that Gronk will be Gronk with that kind of injury is a bit far-fetched.
Unless Gronkowski is even tougher than we think which seems impossible.