FWIW, Palpatine also came back in the original storyline past ROTJ before Disney retconned the EU. Though they didn't gloss over the "how" bit (he always intended to survive forever and had a clone factory hidden on some planet and used something similar to the force ghost, only he was able to posses his clones).
In the original story, he threatens Luke and his friends while Luke is alone, so Luke goes, "ok I'll join the dark side", gets some training, then switches back the first time he gets ordered to do something he didn't like.
The basic message was "turning to the dark side was only so final for some Jedi because the order itself considered it something that couldn't he undone, while Luke did it easily". Some of the video games touched on this, too, where the light side and dark side were just tools and it was how you used them that determined good and evil. It was also a big theme in ROTJ itself, though not heavily explored after Vader turns back.
There's hints of this in the sequels, but IMO they didn't handle it that well, especially with Luke and Kylo.