I'm going to tell you what you know already. Everyone is different. It helps to have a 'good' upbringing, by which I don't mean affluent, but the sort of FOO that has instilled self-esteem. It's not a magic bullet, but it does mean the A has an idea of the person they'd like to be.
I personally took many years to stop drinking altogether, but I wasn't in the acute situation your son has found himself, and I'm pretty sure if I had been I would have been able to stop drinking earlier through sheer fright.
I know it's hard to stand back, but there isn't much you can do. He has some great personal incentives to get sober, and some medical reasons to stick to it, but time will tell.