You don't need to make "The Godfather Part IV". That trilogy ended.

However, I do believe you could do a non-direct sequel like The Two Jakes or U.S. Marshals, that uses some of the characters from earlier movies but doesn't pass them off as Chinatown II or The Fugitive II.

I think that Vincent's role could be re-cast (Garcia did well and was nominated for an Oscar but it's not such a seminal role like Michael or even Vito, which had 3 actors play the role) and a new movie, or book, or whatever, could explore what happened to Vincent and the remaining Corleone family after Part III.

You don't need Pacino. Mike likely secluded himself after Mary's death. Vincent likely allowed Mike's guys to retire and brought in new guys, guys he knew from the streets. So a new cast.

With all the Corleone connections, Vincent could get into drugs, politics, banking, etc. I think you could contrast Vincent with Michael to have Vincent always showing his emotions, whereas Michael suppressed them and wrote off his vengeance as "business". Eventually it leads to his downfall. FFC said that a Part IV was going to parallel Pablo Escobar's downfall. The same could happen to Vincent, and the the series would REALLY be dead.

Get James Gray to write and direct.

I don't know. I never say "die". I'll always welcome the opportunity to go see a new movie in the theater that exists in the Godfather universe.