Wlad needed a hands-on, compassionate, fatherly master to rebuild not just his career, but his confidence, which was nonexistent and destroyed following Brewster. Steward built Wlad back up as a man. Without him, it is safe to assume he doesn't survive Peter.
I think that Wlad would ultimately have built up some kind of momentum, but it would not have led to the dominance that we have seen. Steward was crucial to his transformation, but part of it was Wlad. At some point Wlad sat down and said "I have to make this work".
Depends on who else was hired to take over his corner. Freddie Roach might have been able to do something with him, assuming he was available. But as Janitor said, part of it was Klitschko's determination to succeed. Few fighters have taken three bad beatings like the kind he took against Brewster,Sanders and Purity, then rebounded to have an all time great career.
Waldo always should have been where he is now, but he needed the confidence, inside fighting and defence to get where he is. Other trainers could have guided him there but he certainly needed guidance I think
Steward was an excellent trainer but like most trainers, he trained hundreds of fighters that never amounted to much. The point is, it is the fighter that makes the difference. Wlad would be just as good with or without Steward. Example: Charlie Goldman trained Marciano and got all kinds of recognition for it. However, Charlie Goldman also trained hundreds that did not make it. Steward and Goldman's abilities were the same for all those hundreds of fighters. Vlad and Marciano and many other champions got to where they got because of thier ability, not the ability of their trainers. Trainers that a fortunate to come upon a great fighter, gain recognition for it and they wind up having quality fighters coming their way. Steward had Hearns and he wound up with some good fighters because of it. Angelo Dundee had Ali and he wound up training Sugar Ray Leonard etc.