I've been racking my brain, trying to come up with one, but can't seem to do it. Anyone else have ideas?
I have a fairly broad notion of how a "final" story can go, and some have disagreed with me, but I think a final story can wrap up long running themes and give closure to characters without ending their overall story. A good example of this is Grant Morrison's "World War Three" arc in his JLA run. It's such a big story with an end-of-days type of villain, and it has various character beats where a character either really gets a shining, definitive moment or they overcome their main inner obstacle. so even though the team is still active at the end, for me that is as good a final story for the entire DCU as we could ever expect to get. It's just that good imo.
Very similar to that is JMS's "Happy Birthday To Me" arc in Amazing Spider-Man. Definitive moments, closure, and basically a new beginning, but for me, although the story didn't "end" Spider-Man's career, it makes as fine a conclusion as we are ever likely to get.
Then there's Reign, by Kaare Andrews, which is intentionally a riff on the Dark Knight Returns, but is also extremely good outside of that context. That is a fantastic story that does, in fact, present the very end of Spider-Man's career.