I am not sure this matters. How are we going to argue his legacy in 15 years? If he leaves and goes to another team and wins 4-5 more championships
He is not going to win 4-5 more championships no matter where he goes.
You don't know that. Especially if he forms his super team anything is possible. I agree it's not likely, but if that were to happen history won't remember where it happened, just that it did happen.
Some folks think that when you turn 30, life is over. While that is true for many of us, professional basketball players are taking much better care of themselves these days and can be quite productive to age 35 or even older (witness Dirk). Even broken-down Wade carried the Heat in a few playoff games this year.