I hope we all know that the entire trilogy went through with Al Pacino showing in all three movies even if he was not the star actor?If the great writer was around he would not see it to be interesting making the continuation of his book without Al.
Moreover,in the Godfather 3 I saw,michael didnt die.He only walked away at the end of the film.Let me know if there is another version that shows that he died.
Cheers