Do I neuter a sick cat?

I have an almost 8 mth old kitten. A few mths ago his liver counts were off the charts and ultrasounds found a congential defect where an abnormal membrane is growing on his small intestine-blocking his bile duct. Eventually the vet tells me he will not be able to keep food down & he will waste away. Thankfully I have not seen evidence of this yet (although he has chronic giardia and roundworms). Due to the liver counts (and a "non-threatening" heart murmur to boot) the vet said that it is not safe to neuter him. However, the cat is now consistently gaining weight, is no longer jaundice, and is a happy, loving boy. I am thinking about retesting his liver counts again to see if they are down and if it is worth neutering him as I live in fear of spraying (do ALL male cats not neutered do that?). I lost a cat unexpectedly at a vet once so am scared. Do I leave things as they are as my kittie is doing well for the moment or do I take the risk and neuter him (I have 2 other boy cats!)