In which Luke is just a Perfect Angel and literally cannot be evil. Even if he wants to be. Even if his father and maybe even sister tried to lure him to the dark side.

Exasperated!Vader still wanting his son to rule the galaxy with him (and Leia if he knows about her) but Luke keeps wandering off to rescue kittens and read stories to children and stuff.

Bonus: Vader lets Han live because he was so willing to protect Luke, which he appreciates. So Han's kept around as Luke's bodyguard/companion.