I'm so sorry, Cyn. You know me....if I were Zane's caretaker, I'd do whatever I possibly could, as you are.
Something that really helped me in the past, and maybe this will help you, too...I had a dog that had severe hip dysplasia. When we took her to the vet to find out what meds to put her on, we asked the vet what would happen next, and she listed what we would see as she went through this and got worse. DH and I made a decision that when our dog got to a certain point in her degradation, that it would be time to put her down. We watched all the signs the vet told us would happen, knowing we were getting closer and closer. Finally, the day arrived when that one thing happened. We looked at each other and knew that was the day to help her pass.
Maybe you can do the same thing with this situation with Zane? Decide if he gets too bad, to a certain point, if something were to happen...I dunno. I'm not an eloquent writer or speaker, but I'm sure you know what I mean. I think sometimes, it makes it a bit easier and comfortable to accept if we decide in advance. Know what I mean?
That being said, here's hoping he NEVER gets to that point!