I don't think UTIs and stones in a younger kitty are USUALLY causes for euthanasia. If you choose the food and kitty treats wisely, and make sure he gets lots of fluids (adding warm water to mush up some wet food a bit helps), then handsome Irwin should be with you for many years to some.

Shortly after I got my tabby Oscar a few years ago, he developed a nasty cystitis. There weren't many crystals - and those that were there were gone in a week with a change in diet. However, there was blood in his urine up to a month later.

In addition to changing his food, my vet said I could use the powder from a cranberry capsule. About 50 mg - or 1/5 of a capsule, as I eyeballed it - went into a small amount of totally plain unflavoured low fat yogurt. Oscar loved that stuff, and got the cranberry in with it. It was to be used for about a month. (You can ask your vet about this).

Hugs to you and to Irwin, and I am sure you will be able to maintain his new health for a very long time.