Which makes a case for young males to stay in the group as long as possible, mating with an younger animals that is less dominating and a chance of rearing my help later coupling with a silverback, when the black male is removed from the group?
Mating with a younger(less threatening) male is certainly the way some desocialised females get pregnant. But I think in instances like that, even after a successful rearing, its unlikely to result in changing the relationship with the silverback. The female who won't let a certain male mate with her remains that way for good.
I think the longer young males can stay in their natal groups the better, for all reasons- but primarily their own social benefit.