My friend's cat just died recently, she was twenty years old.
I wonder if the cat would have lived longer if she was fed real food.
I sympathize-- as they get older, they can get a little high maintenance, but you love them, so what are you gonna do? My old cat was 19, and actually in very good shape (just a rare occasion of peeing in the corner........), though I was dreading the day her health started to deteriorate. Anyway, we came home one day to find that a dog had come into the yard and killed her. She obviously was caught unaware and didn't have time to retreat through the cat door. It broke our hearts. Yet, I have to admit a small part of me felt a little relief that I didn't have to go through the torture of watching her health slowly decline.
Maybe you'll get lucky and the vet will have some ideas for you. Good luck. Hang in there.