Well, just as a thought experiment, imagine the implications of other endings--
For example:
1. Tony dies--some one else takes over and life goes on.
2. Family members die but not Tony--same thing
3. Tony goes to jail--life goes on someone else takes over
So, it doesn't matter what happened to Tony--this is not a fairy tail or a Nancy Drew mystery--
Anyway, I can't think of how any other proposed ending would have been any better
Consider, for example the Godfather ending--the aging mafioso sitting lonely on his chair--but the whole world still goes on.