I agree with Don Al DeBrando, his post perfectly echo's my impression of the scenario's outcome. Vincent went through a big transformation in GFIII, from an unsophisticated hoodlum who knew "certainly dressed for it" to a much more calm and sophisticated person, this is evident through his manner by the end. However, he was a hot headed individual at the beginning, brash and quick tempered. But he certainly learned. He had loved to Sophia's Character, pretty deep love, but he did give it up, which was the intelligent move. Now if he totally followed Michael's ways he would wait for Michael to die to have her, but that's neither here nor there. I think the key to his personality change is in this act. Why? Well because Sonny never overcame his temper. He didn't do the right thing and it was a fatal error, when he went after Carlo for the second time in GF1, in that case Sonny was ruled by emotion, but Vincent made the intelligent choice, which meant he conquered his battle, mind vs emotion or at least learnt how to keep it in check.

In that light, I feel Hagen would have been disapproving or apprehensive at first. I think by GFIII, he would have enough faith in Michael to trust his instinct and it would have been a subtle point, adding further depth to the story and intricacy... only if FFC choose Duvall over a staircase... WHY? WHY?