My beloved Boo-Boo, black male cat, was diagnosed with kidney disease when he was 14. The vet emphasized at the time that while incurable, he may very well die of old age rather than the kidney disease. The diagnosis occurred long before I researched cat food and switched the cats to a raw food diet, so Boo-Boo never got that. I did put him on the vet-recommended Hills k/d formula, supplemented by occasional bits of tasty chicken and fish - which, of course, he just loved. Towards the end, we did have to start hydrating him with the i/v fluids, but it wasn't bad once we, and he, got used to it and it always perked him for a bit afterwards. When he started having trouble with his balance and walking and was less interested in food, we finally had to make that last, difficult decision - but Boo-Boo was then the ripe, old age of 19 and he lived a long, happy, loving life. Best wishes to you and your feline friend.
2001 Trek 7500 FX, converted to a hauler - Serfas
200? Marin hybrid - Selle San Marco
2004 Trek 5200 - Avatar
2011 Trek 6.2 Madone - Ruby