Michael cashes out, bestows lots of money on Kay, Anthony, Connie, Neri, etc., and lives in seclusion in Sicily until he dies like a dog.
Vinnie goes back to the Street cause thats what he knows, and maybe rehooks up with Brigit Fonda.
DT, I agree with all you suggest except Vinnie's role. I think Vinnie would have tried to continue the hegemony of the Corleones in NY, but would have been successfully challenged by the other families.
