The dead don't always stay dead. This is a lesson I learned early on in fiction. I read Sherlock Holmes, who may not have been the first hero to die only to be resurrected, but was surely one of the most famous and probably one of the first instances of the "fans" keeping something alive. (There are a few other parallels with Star Trek I could mention, but those will keep for another time.)
For those who don't know, Arthur Conan Doyle got tired of his consulting detective after the initial run of short stories. Feeling the character was at an end, he crafted a suitable ending for Holmes, letting the detective meet his end locked in mortal combat with his nemesis, Moriarty, at Reichenbach Falls. Having penned and published the story, Conan Doyle moved on to other projects. The fans would have none of it, and eventually Conan Doyle caved in, resurrected his hero - who it turned out had only faked his death - and went on to write more stories. Holmes wasn't done yet, and did eventually earn his retirement as a beekeeper in Suffolk (or was it Suffix?), England.
Sometimes, characters just won't stay dead. Comics are notorious for this, Spider-man's parent company Marvel in particular. No one stays dead in the Marvel universe, not for very long anyway. Which, in my opinion, has lead to some rather silly things and has robbed death of much of its impact. Yeah, they killed Captain America. Whatever. You knew they were going to bring him back eventually. Heck, they brought Bucky back. (And if that makes no sense to you, consult the Wiki gods.) So if you do this in your story-telling, you run a very real risk of boring your readers. They know their beloved character isn't really dead, after all, so it's all kind of ho hum.
You can't even keep the shock value of a good death going if everyone knows it's not going to stick. (Even if it should, Marvel comics being an example yet again of having brought back a few people I thought should have stayed gone.)
I think there are times when death and resurrection serve as appropriate motifs. Sometimes a role just isn't the same when another person takes up the mantel, say in the case of the new Batman. (Though I am reserving judgement.) You run a storyline with someone filling in, but eventually that runs it course and the main act needs to return. Achieving that return is tricky, and can be as alienating as the original death if either of them is handled badly.
All that said there are moments when the sacrifice of a character serves a need of the plot, as well as their return. I think in those moments it's important to have the character come back slightly different. You don't get to die and come back unchanged. Gandalf's demise in the first part of the triology still has tremendous impact on me, even though I know every time I read/see it that he's going to return. In part it's because Gandalf the White isn't quite the same as Gandalf the Grey, and so something was lost in that death.
Of course, if you right in the right genres, death never needs to be permanent. There are always clones or zombies.
Though I don't know that anyone has ever done zombie clones, or cloned zombies. Might be something to consider.