The best end would be if Vincent manage to do what Michael didn`t.
Michael wanted to get out of the crime scene. To be a legal and respected business man who loves, protects and lives in harmony with his family.

Vincent might feel guilty because of the death of Michael`s daughter. He get`s some wake-up calls and flipps over to be a good Don.
But first he needs to kick some ass. He needs to get rid of the other families and gangsters once and for all.
In the end he should be feared by criminals.
Respected in the business world and even by the goverment.
And loved by the people.
He should become the Don that Michael dreamed about to be but never became.