My son too has a diffuse axonal injury. While everything that you read on the internet tells you that this is the worst brain injury you can have (which it probably is) don't believe that your friend can't get better. My son was also in a car accident, mid july 2011 (he had just turned 17). He was dead at the scene and they were not able to get to him due to the severity of the crash. He had a seizure which brought him back to life... although I know that the Lord was in control. He was in a coma for almost a month and in ICU for 49 days. He was then transfered to a Pediatric Rehabilitation Hospital, where he spent 6 months as an inpatient. He too breathed over his ventilator and they didn't remove the trach until he was in the rehab hospital (not long after he was there). He was not able to move anything on his right side, including he could not look with his eyes to the right side. When he went to the Rehab Hospital, it took 3 people to move him into a wheelchair. He couldn't follow any commands, he couldn't even open his mouth. He made no response to us at all. He was on a feeding tube, etc... We asked the doctors about his recovery and they told us he could go anywhere from 0-100% recovery.
It's now been 9 months since his accident and he's made awesome progress. He's able to walk on his own (I don't let him go completely unassisted
) He can feed himself, he helps dress himself, he too does the thumbs up/down; but he's beginning to communicate via my IPad. (He still doesn't speak, but he does make a lot of noise).
What I want you to know is that your friend can recover. No the doctor's have no idea how much brain damage there is... yes there is brain damage (each of those axons is destroyed and will not repair itself), but there is so much about the brain that the doctors don't know and it's a miraculous organ.
My son has an awesome rehabilitation team. It's all about him!!! They think outside the box for all his therapies (PT, OT & Speech).
Talk to your friend, let them know what happened, tell them what is going on around them, show them lots of photos, etc...
He will go through a stage of agitation that you have no idea why, but remember it's temorary. It's actually a good thing, it means that they are beginning to realize more and more and are frustrated that they can't change the circumstance.
This is going to be a long road, but remember with lots of love & support they can get better. Maybe not to the exact place they were before the accident, but much better than where they are currently.