Filou became 12 two weeks ago and he is still a little bit further from where Puddy is now but I see it just like you- as long as they are happy and eat and purr I will do anything for him.
But for sure I will not put him through a transplant- what is a 50% chance for a life of some years that could not be an easy life- looking at the meds they would need to make the transplant work.
Filou doesn't like meds- NOT- AT- ALL!!!
So I try to feed him as well as I can and to enjoy that he is around, even enjoy it when he is naughty which he preferrably is at 3 a.m.. He sends some deep purrings to Puddy.