These are just my opinions found through my own experiences.
I think a few more questions should be thought about------Does he want to quit drinking? Is it causing problems in his life? Things like that. How does he react when you encourage him not to drink? Positively or negatively?
I don't know if there is a right or wrong answer. Basically, he will have to decide and when the time comes, hopefully, he has a good support system.
I'm trying to reconstruct my life after many years of drinking and isolating. I'm an introvert so I thought I found the solution to "fitting in" because I could be more outgoing when I was drinking, yada, yada, yada.....not a good solution for me.
Maybe someone with more experience can help you with an answer but that is what I can think of off the top of my head.
I hope everything works out okay.