Scruffy said:
Whether Vader won the fight or not, he was still an emotional wreck, a dark side dilettante, and a willing slave of the Emperor. His trajectory would not have changed very much. Yoda and Bail Organa would have come up with different arrangements for Luke, but that would not have changed Yoda's endgame of training him to assassinate Vader. It probably would've happened sooner, without Obi-Wan's sentimental notions of avuncular rights.
How would they have gotten Luke? Anakin would have walked back over to Padme, seen her alive, and the kids would be in his hands.