It seems very unlikely that all three will resign, because the Democrats are well aware of this. The bigger issue is that he can't run for re-election if he becomes governor, and even if Northam or Fairfax sticks it out, Herring may well be too damaged to win.
As I said at the start of the thread, I think Northam would resign, though he's so far sticking it out.
Fairfax depends on additional allegations. In #metoo, all allegations I am aware of that were not intimate partner allegations were ultimately followed by several more, except in one case: George Takei. So while it seems unlikely that Fairfax will be the second exception, I am willing to give him the benefit of the doubt pending more allegations.
As I've said, I don't thing Herring should resign, but the Republicans are making hay of this and almost certainly will keep doing so until the elections this November. I imagine the main goal is to demoralize black voters, because if they feel like the Democrats have failed them and don't turn out, Republicans keep both houses and even expand their majorities. If they win a few swing voters over as well, that's gravy.