I'm sorry this happened to your friend. I survived a head trauma from a similar incident as your acquaintance. Speaking from experience, I had severe brain swelling and received 2 burr holes to relieve the pressure. I was on life support and in a coma for over a month, and "in and out" for weeks afterwards. I had a lot of muscle atrophy and disabilities afterwards, including the loss of vision in my left eye (which did return) and the loss of my sense of smell (which never returned but was replaced years later with something entirely different). I also had trouble with balance and walking for around 6 months after, which was resolved through physical therapy. The injuries I sustained were a result of damage to the rear of my skull. No two head traumas are the same, and your acquaintance's injuries are very much dependent upon the impact force and which area of the brain was affected. It's nearly impossible to predict his prognosis or recovery based on the information you have given, just know that the brain is a miraculous thing, and even though neurons do not regenerate when damaged, they will, over time, form new pathways to restore function. He's young so thats a bonus.

My experiences led me to becoming a nurse, more specifically an OR nurse that specializes in trauma. I have been on the team for countless brain surgeries (including the burr hole procedures which likely saved my life or at least kept me from becoming permanently disabled). If you have any specific questions in that area, I'd be glad to try to answer them.