What if Nellith Skywalker was real?
We know that in the original concept, Leia was not meant to be Luke's twin; instead, that role belonged to Nellith Skywalker, who was training as a Jedi elsewhere in the galaxy. Due to George Lucas's personal and health issues, her storyline—originally intended for future films—was cut, and the role of Luke's sister was given to Leia.
How would things have played out had Lucas stuck to the original idea? Would Vader and Palpatine have died at the end of Return of the Jedi? Would one—or perhaps both—have survived to serve as the villains in the subsequent trilogy while Luke traveled the galaxy searching for his sister? If Vader had survived, would he also have sought out his daughter to turn her to the dark side?