In the LOTR example it was handled in a believable manner, which is part of what makes it so damn good. An object so infused with evil that it even corrupts the person who owns it, as well as the means to resurrect the dead Lord to whom it belongs? Freaking awesome! What an incredible plot device to drive a story.
Palpy was killed off in ROTJ in a way where there was no reason to question whether he survived. He was dead. Plain and simple. It's been like 20 years since I even thought about Dark Empire but to my vague recollection it was a younger clone of Palpy that came to fight Luke and company. Like I've said though, I was never very big on that series either. Mostly because it undercut the victory at the end of Jedi.
This movie though? There was no clear explanation
in the movie for how he survived so to have him shoe horned into the last movie just to have a big bad to fight off is ridiculous when if you were to watch the films chronologically Palpy would just show up out of left field. And using a novel, comic, video game, cartoon, toy, trading card, cereal box, etc to fill in vital information because it's missing in your script is direct evidence that there is a FLAW in said script.
Purposefully omitting key information to create mystery is not the sign of a talented director, but the fingerprints of a master manipulator who tricks audiences by giving them the impression that what they witnessed was somehow better than it actually was. JJ, as
Solo4114 has so eloquently stated through the years, is a master of this technique. If you loved it that's perfectly fine, but a more honest response would be to acknowledge that you could see the issues with the story, even if you ultimately liked it. Being a writer I can't overlook glaring issues that take me right out of the story. Especially when it's one I'm so attached to. Other people are willing to overlook things like that. I'm not. At least not with these characters.