We had to have my wife's 12 year old kitty put to sleep this week after he fell into the bathtub and injured his neck. He couldn't walk well or take care of himself.
Whenever anyone has a pet, the best we can ask for is that they have a long, good quality of life. But all pets, like all people, have a specific lifespan. When their health goes south, we just need to accept it and do what's right for them and their families. It's just always so difficult to say goodbye to a family member. But when it's time, it's time.
We also have a 2 year old Maine Coon Cat, and he's quite a character. It's hard to believe that by the time it's "his time," we could be elderly or invalids and it could also be "our time."