Not much can be done. He either will die or won't die. To take that quantity of drugs intentionally would go beyond a "party" mentality and implies that they probably wanted to die anyway. There's really nothing that we can help you out with specifically, seeing as how we are a Harm Reducion forum and this is only the internet. The best thing you can do is to locate your friend (if he wants to be located) and to get them emergency medical attention.
There's definitely not a lethal-dose that will work for everyone. The differences can be exponential, so for right now, you need to work on find your friend and getting them the help they need. We'll be here for emotional support if needed, but in short, this could definitely kill someone. It wouldn't be surprising in the least.