According to Wikipedia, there was once a common expression that "the only people who stay dead in comics are Bucky, Jason Todd, and Uncle Ben." By now, the first two were also resurrected. On the other hand, as far as I know, Gwen Stacy (of Earth 616) remained dead for good.
Of course, I'm sure that over the years there was a multitude of minor characters that died and remained dead. So let me formulate the question as follows:
Are there other prominent comic book characters, in Earth 616 (Marvel), that have been dead for more than 10~15 years, and are still dead now?
I realize that "prominent" is a bit subjective. I'm looking for characters that were an integral part of the life of a person who had their own title, like Gwen Stacy was to Peter Parker. (In fact, I'm not sure Uncle Ben himself counts, because I think he was dead before the title of Spider-Man began). Of course, if the very person with their own title died and remained dead (e.g. if Spider-Man or Captain America had not come back), that's even better.