I remember when I started reading comics, around 1993, the saying was "Nobody stays dead in comics, except Uncle Ben, Jason Todd, Barry Allen, and Bucky". And that actually stayed true until around the time I stopped reading comics regularly, almost a decade later. So... Uncle Ben's still dead, right?
But the revolving door was already a joke by then, with just a few specific characters staying dead, either because they were part of hero origin stories (for Spidey and Captain America), or because their replacements had become popular enough that there was no going back (Wally West and Tim Drake).
And no, I don't feel bad talking about Marvel characters in with DC here. The topic of this thread isn't company specific.