Maybe consult an interventionist beforehand. I would think a good plan that all parties are on the same page with would be optimal. I don't know if the friend has experienced any significant consequences up to this point but if not then this intervention should serve as a starting point. The consequences have to have meaning to the individual so consider that also. Marriage, job, social standing etc... most all have probably been touched by this time but if everyone has held their tongue or tiptoed around the subject then it may be time to set out some rules for further engagement. Wife not going to wake him up when he oversleeps, friends not coming to get him when he can't drive and call a Uber instead. Eh, hope you get the idea. People have to be somewhat committed to their role in the plan I think for the best outcome.
Was told in a meeting early on that you can lead a horse to water but you can't make him drink. You CAN however show the horse how refreshing the water is, how clean it smells, how cool it is to the touch. Make the horse thirsty.
And don't forget consequences, it's all about the consequences.
Good luck and Gobless.