Maybe Luke and Vader could’ve briefly talked about the Empire during their conversation on Endor. It could’ve paralleled Luke and Obi-Wan’s conversation where Luke says, “I don’t like the Empire but there’s nothing I can do about it right now.” Luke challenges Vader to do the right thing like Obi-Wan once did to him, and we could’ve gotten insight on what Vader thinks about the Empire, but give an excuse as to why he can’t change it. Maybe after he killed the Emperor, he could’ve stumbled over to the Emperor’s throne, with Luke looking on worried if he would sit down to “take the throne”, only to have him call off the attack and order their forces to retreat. Or something along those lines. If the rebels were losing, and Vader’s orders saved them, it would’ve helped tie Luke’s act of nonviolence not only into saving his father’s soul, but also save the Alliance (especially since their ability to destroy the shield generator and then the Death Star is rather disconnected to the battle between Vader and Luke).

I honestly thought Kylo Ren’s redemption was meant to set up a similar idea. Having him become the Supreme Leader, but then to turn back to the light, would’ve allowed him to finally end the war in a nonviolent way. Unfortunately we didn’t get that.