I get it but can't a transplant actually work well for him ? I've just read the statistics and they seem really decent. Perhaps he "needs" anti depressants and go for a transplant. It's not clear to me he is in a completely lucid state of mind - he is saying himself he thinks he has PTSD, plus he has a bunch of stuff to live for it's not like he hates life - he just hates this shitty medical mess he is in. However, it looks like his family is on board with him going through with this so what can I say.
A transplant always is a life altering change. You'll be on immunosuppressants for the rest of your life which has a massive impact on your quality of life - and that's _if_ you get a transplant before you die.
I have no idea how I'd react in that situation - but I can understand people who'd rather not. Especially considering that you might not want to take one of the few organs from a person who might be willing to fully commit to that.
When reading the rest of his posts, I think you are right to ponder how his mental health is negatively impacting his outlook. He seems to be more ready to accept death than I'd expect, given how young he is. I wish him and his family the best; an unimaginable situation.