I think I figured out what's gonna happen
Goku can't fight Black because dude has that bullshyt saiyin stuff about getting stronger after/during any battle. But at the same time, its like he's absorbing all of Goku's techniques everytime they fight. The only person Goku can kill here is Zamasu, where he'll have to incinerate that guy like they did to Cell.
Its all up to Vegeta to kill Black.. but watch its only gonna be after he dam near kills Trunks and/or Bulma. Breh gonna get that rage boost and give him that work
Vegeta made Black stronger and fed him new shyt too when they fought before Black shanked him.
The only way Vegeta is getting that final W is if he's fused with someone else. Best solo case, he'll get his ass kicked to bide time (again) while Goku works out the mafuba or whatever technique gets invoked to take out an immortal
that is likely to be fused with a souped up Black at that point.