I wish him and you well. I watched my brother through four months of hospital horror including eight weeks IC after the hospital "gave" him a very rare type of infection during a tiny op. He didn't need a transplant, but did need a new aortic valve after infection damage, and lost some toes.
He was an enormous 38-year-old, and is now an enormous (again) 40-year-old, having regained the lost six stones. Once he was out of hospital, eating well and moving around, interacting, the improvement was remarkable, both physically & mentally. He seemed better almost by the hour, and I'm sure you'll enjoy seeing this happen with your son... best of luck