Honestly I never really liked the idea that someone as evil as Vader could be saved. If Luke had succeeded right away and he and Vader took out the Emperor…what then? Vader doesn’t pay for any of his crimes? Because if he is going to pay for his crimes, he’s either going to be executed or spend all the galactic years of his life in prison. And if he’s not, well then what?
Same thing with Ben at this point. It’s too late.
In the Infinities comics, Vader gets a new suit and apparently joins the Rebellion.
I find this interesting, as I had the crazy idea of a Trek Mirror Mirror type Universe when I was a kid, where the Empire was the good guys, and Vader wore white.