Sorry this has happened, Bb. I know how you've struggled to be supportive, but it's time to take care of yourself.
They disappear because they are ashamed. They DO know they've let people down. Of course, alcohol helps them numb those feelings away, so they are incapable of acting on them.
It sounds like he's just not "there" yet--whereever he needs to be to completely surrender and get well. There's no way of knowing when/if he WILL be ready.
You will find out what happened eventually. I seriously doubt he is dead somewhere (yet). He is probably holed up at a friend's house, or in a motel or a shelter.
It's very hard to give up hope, but you will have to accept that the hope of his recovering in the immediate future is pretty slim. So you should start thinking about where your own limits are. Do you really want to go through this whole deal again? As much as you care about him, can you put yourself through it again?
When my second husband went back to drinking after almost dying of liver failure, it was hard to accept that he would rather die, apparently, than do the work necessary to recover. Still, that was his choice and I could do nothing about it. As much as I cared for him (and I still do), I had to get away for my own sake. Yes, it was sad, but much better than having to watch it every day, being helpless to stop it.
Hugs, sorry this has happened.