If they're able to make a part IV that's as good as I or II, then sure. I would love to know what happened to the Corleone family when Vincenzo rules, and also I would like to know about the years in between the flashbacks in II and part I when Vito builds up his empire, with the help of Luca Brasi.
But since Puzo died, I know it wouldn't be a good movie.
D.M.L