I hope your buddy recovers quickly with no lasting effects.
Something I wanted to bring up, I was reading a thread on Reddit where a Military guy who was in an induced coma talked about understanding a lot of what was happening around him while in the coma.
I highly recommend visiting your friend in the hospital if you can. There is no proof but I believe all the friendly voices will help his recovery. Talk to him about the good times to give him something to focus on other than the nurses, tubes, and pain.