Haven't had any of my fish that long. Still have all of my first fish, six black skirt tetras. I have nearly all of the fish I've bought yet.
I may be rescuing two of the most abused yoyo loaches ever soon. They survived a cycle without water changes, and have survived for the intervening five years with no water changes, just evaporation top-up with tap water. The pH crashed long ago, and they're still plugging at a pH below 5 and a hardness higher than I could measure. Everything else that's touched the tank has died in days, if not hours, and dead tankmates have been the loaches main food source, since the owners have only fed goldfish flake to the tank.
I'm afraid I'll kill them in the process of trying to save them, to be honest.