Someone mentioned characters coming back further up and your post had me thinking about characters who ought to be dead in a final way being resurrected. The big example for me is Ian Malcolm in Jurassic Park. Malcolm (and the book in general) are tremendously important to me in a way I can't articulate at all. So the fact that Malcolm is inexplicably alive in The Lost World should be pretty awesome from my perspective, but I'm forever put out about it. I suppose it cheapened whatever emotional response I had to Malcolm's death. I actually couldn't tell you at all what my response to Malcolm's death was, only that I must have had one, else I wouldn't be so annoyed about his resurrection.* Of course, I can console myself with an entire book about him.

*I do get hung up on details often. But I forgive the unexplained time travel in Cryptonomicon that results in plot holes big enough to drive a truck through.