Sonny, because this question has been asked and wondered about by so many for a while, I think I should answer it for everyone. Mario did finish Omerta before he died, but it was his habit to rewrite a manuscript several times before the final version. On the Last Don we had 17 rewrites. But with Omerta he had just finished it two weeks before he died and so he hadn't the time to rewrite those few extra times which would have possibly put a polish on it.
I didn't finish that book for him because I was brought up by an Italian father in a patriarchy so I understand the system. For me Mario's books were male myths. I probably would not have had the women, Nicole and Cilke's wife, play such a major part at the end.
The truth is that if the author isn't around, the editor of the publishing house gets to correct it.