The thing with "The End" stories, especially when it comes to Spider-Man, is that many many many writers have already done this concept to death. Happy endings. Sad endings. Endings where Peter dies. Endings where he and Mary Jane have children and live happily ever after. Endings where Peter's... "webbing"... causes Mary Jane to die of cancer. One "ending" had Peter becoming a police officer.
I think it's so difficult for you to come up with an idea is because it's all be done before already.
As far as I can remember the only "ending" style story they haven't done is one where Peter dies due to some mundane reason. Maybe he's fatally shot by a burglar (which would be ironic) or maybe he dies of an incurable illness. Something that real people deal with every day that cuts the wall-crawler down despite his powers. Kind of like when the original Captain Marvel died of cancer. It was a powerful story because no matter how powerful Mar-Vell was, he couldn't stop himself dying from disease because there was no cure.
In other words, sometimes a hero is at their most heroic when they are at their weakest. Everyone tries to do a "Hero defeats all his bad guys, gets the girl and lives happily ever after" that's old hat. Doing a story where a character comes to terms with their own mortality and dies with dignity? That's something you don't see very often. Maybe once every 40 years or so.
What is it with people your age and your interest in the fates of heroes being 'realistic' and mundane? Are you own lives much more believably hollow that unless a hero is living that life with you you can't identify? Try to have a spark of optimism Mr. Edge.