James Bond and Batman will not retire as long as people keep watching James Bond movies and reading Batman comic books.

Harry Potter defeated the great enemy wizard at the end of the seventh book, and is done (although he then started his career as an Auror, hunting down bad guys). Dorothy Gail came home to Kansas to stay (but then featured in sequels). Tarzan settled down with his wife at the end of his second book - out of 24.

Similarly, none of my characters have ever retired when the DM had another adventure for them.

Let's face it. For an adventurer, retirement means settling down on a small plot of land - about six feet by three.