I actually think he will retire either way.
He isn't coming back to Tampa for another season with that staff, and I can't see them firing another coaching staff just to appease Brady for 1 year.
So then, it's starting all over somewhere else at age 46 on what would almost certainly be a 1 year deal. Forget Brady, from the new team's perspective that would seem like a waste of time.
All that said, I fully expect that he will be playing in the Super Bowl this year.