I doubt it. Coppola certainly could have gotten financial backing even in the late 1990s, and there's some evidence of at least the rudiments of a plot outline before Puzo's death.
That plot outline was ALLEGEDLY used as the basis for Ed Falco's "The Family Corleone." But Paramount showed absolutely no interest in adapting it into a fourth film. As a matter of fact, they tried to sue the publisher for copyright infringement.
"I got news for you. If it wasn't for the toilet, there would be no books." --- George Costanza.
