I say Neil would be accepted as boss. Paul or Joe Gallo could be acting boss before he gets out.
The family would still do well financially under Neil. Everything was pretty well established.
The Commission case might have played out a bit differently, but would have ultimately come to the same result. Law enforcement was closing in. Dellacroce was tied to the murder of Galante.
Gotti wasn’t made in 1976, but I can imagine Neil making him underboss eventually or at least his successor when he dies in 1985. So then Gotti takes over and things play out pretty much the same as in real life.

The big question would be what would have happened with Castellano?