I believe scenario two would result in scenario one. As for Scenarion two, I think that Luke, having been raised on Tatooine would become a regular Jhorus C'abaoth. he would rule over his own, small area, and stay away from the Empire since he dislikes it. He might try to get Vadar to come over to his side, though I doubt it. The other possibility is that he would form his own Sith Lord faction, build up lots of strong force users, claiming that this was all Jedi training, and not to worry about the fact that all of the targets were alive, thus turning the galactic civil war into a three-way civil war. Luke vs. Empire vs. Rebel Alliance vs. Luke. Everyone is everyone's enemy!