An alcohol overdose would depend on how big of a guy he is, rate of metabolism, rate of drinking (even though you know the time frame within which he drank, we don't know if he downed more drinks at a faster rate during one hour than another). The amount of alcohol that causes someone to pass out is usually dangerously close to the level that would cause alcohol poisoning. It's important to remember that klonopin and alcohol affect the body in similar ways... they both increase the amount of the neurotransmitter GABA (which decreasing the rate of brain signals). The effect of this is that klonopin increases the effects of alcohol and alcohol increases the effects of klonopin. The use of klonopin OR wellbutrin with alcohol can pose a risk of seizure, and he took both of these meds, which only doubles that risk. And as I mentioned before, his breathing can be depressed enough so that he isn't breathing at all... leading to brain damage or death.

Because he's "sleeping it off," it's going to be hard to tell what's going on there. There's little difference between just a drunk person and a person with severe alcohol poisoning when they're sleeping. Ideally, because of his risk for drug interactions, alcohol poisoning, and head injury, he should be monitored in the ER. But if your friends are going to be stubborn about that, they will need to wake him periodically in light of the alcohol consumption and the head injury... if he does not wake up, or if his skin is blue, cold, or clammy, or if he is breathing less than 8 times per minute, or goes 10 or more seconds between breaths, or has irregular breathing, or vomits while he sleeps and doesn't wake up, this is a true medical emergency and they will need to call 911. The same is true if any indication of a seizure is noticed, which probably would not be noticed if he's sleeping.