If he was built like Bill Russell, long and lean, or even like Wilt, he would have several good years left.
I just don't see how he can carry that much weight up and down the court for an eight month season.
The only way this can work (and it probably won’t anyway) is to play Shaq sparingly in the regular season to keep the tank full for the playoffs. In the playoffs limit his minutes and pull him as soon as any game has been decided.
Also he needs to spend the entire off season shooting free throws - 100s even 1000s of them everyday until he can do it in his sleep.
Maybe taking a few pounds off would help. Do lots and lots of swimming and other low joint impact exercises.
Doing all of this he might be able to eke out one more title considering his supporting cast.
You forgot the leanest long term center in the bunch - Kareem. Even at the tail end of his career he gave the Lakers some amazing minutes. The man really took care of himself.