I don't know if anyone else has ever said this, but, I had an idea if they did part IV, to make it just a little more Godfatherish, since otherwise it would probably just be like Connie coming back from the old films, would be to say this: Tom was not actually dead in part III, but in hiding for some reason with the help of Michael, and it was all some big fake thing-he just had to lie in front of BJ Harrison in that one scene. So if we explain that retroactively, with Michael in Sicily and Kay out of the picture and Vincent sort of as the new guy, you have Tom come back after all this time to continue as an advisor in the new regime. Since we never actually saw him die, its entirely feasible. And it would be interesting if in the end, somehow, Tom actually does take control of the whole thing.