This is what managers and HR is for. If you're uncomfortable bringing up the issue, explain to HR and have them present it as "we want to help you" and not that "you're in trouble". Depends how good your managers and HR are. It's probably best for everyone that he can move forward with his alcoholism, even for himself.
I'm not throwing my hat on either option, but I am highlighting that this option has consequences you need to be prepared for. (Ok, they both have consequences)
What I have found, are lots of organizations that suffer because they allow a tyrant to exploit the imposter syndrome of those around them.
What you have here is a shitty manager who is holding his company back and putting it at serious risk by not remedying a serious problem. It's exploitative, demoralizing, and entirely unnecessary.
Get this guy some help before he dies. And fire your miscreant of a manager.