Probability that acute alcohol poisoning from isolated binge (bac of .50, can't be woken, 8 hour sleep at er) results in permanent brain injury? how?

Alcohol abuse: It sounds like you're talking about someone you care about .I'm sorry this happened. Pretty much anything can happen if we overuse a drug legal, prescribed, or otherwise. That said it's very difficult situation as usually there's a lot more information that's missing. For example if the person used any benzodiazepine it could result in this. Many other factors. Luck to you and your friend.