We know Vader wants Luke to join him, but it is evident Luke doesn’t want to. He needs the emporer to help turn Luke to the dark side, then kill the emporer, Vader really doesn’t think there’s any light left in himself. Till the end? Does Luke’s speach about his father before him do the trick? It was only when Luke was getting shocked he betrayed palpy. He thought about it too. That was his chance to kill the emporer.
Interesting, and I was thinkin about it, but I have to quote Threepio:
I just really don’t know how.
I can’t put the whole thing together. I don’t know what outcome Vader expects when he turns Luke over, because he must know if he lets the Emperor run the show, than the possible outcomes are not in his favor at all.
I am sure Vader is not sure too. When on Endor, after Luke refuses to join and is led off by the troopers, you can tell Vader was thinking things over. That could have been the beginning of the conflict, maybe second guessing his decision(s). There could be time for him to choose what to do when he brought Luke to the emperor. It wasn’t until the VERY end when he made his choice, which had to be a QUICK decision. Save Luke or not.