As long as Vito lived, he retained the loyalty of Tessio and Clemenza, and their people (except for Paulie). Sonny had made his bones, and was leading forcefully, if not brilliantly. The other guys' attempt on Vito had failed. And, most important, the cops were cracking down on all the families, so there was nothing to be gained by Corleone men if they defected to another borgata. Had Vito died, I'd have serious doubts about whether Sonny, with his reputation for hotheadedness and his gaffe at the Sollozzo meeting, could have held Tess and Clem's loyalty.

In real life, the Commission stripped Joe Bonanno of his donship and put his former close associate, Gaspar DiGregorio, in the chair. The family split almost down the middle because many Bonanno men resented that Joe had made his son Bill consigliere, and Bill had virtually no experience in the family previously. Even more defected when Joe disappeared and the others thought he was dead. They weren't going to risk their lives for Bill. The only thing that prevented a complete DiGregorio victory was that Gaspar was not only inept, but in failing health.