I was just thinking what an articulate and cogent post you wrote, and then noticed your user name, and figure you must be a writer...
I connected with so many things you said... the running away from alcoholism in family of origin; being sideswiped in your resolve to not get involved in alcoholism, but having it happen away; witnessing the sad but inevitable physical decline; being grateful for rooms in the house that can make you feel a little more detached from the craziness; wanting a future with the "sober" half of the husband; feeling completely baffled by his choices; and looking ahead to a big ol' question mark.
You want a window to the future--you see the one path that seems hopeless and sad and another path ready to fulfill your hopes for a loving, healthy family life.
Some of us have stood on that fork in the road trying to figure it out for a LONG time. I hate to discourage you, but in some ways I'm still there after 34 years of marriage. At 58 years old, my AH is still acting like yours--I also heavily identified with having a husband for half a day. It's become a joke in our house. He won't talk about important issues before 11am because he's not a morning person (I am and always try to bring up things at the crack of dawn). But, I'll look out the window (we're both self-employed, too), and his car will be gone at 11:30, and he's off and running to drink for the rest of the day.
So, if I don't say what I have to say in this 30 minute window, I'm scr'wed. Sad, isn't it?
I am pretty happy today, because I have stopped forcing my expectations for a sober marriage. I've also finally dealt with my fear for his early death, which was hard, but I accept what I need to accept.
He's been talking rehab, after I left him for six weeks explicitly because of his drinking, and also because of a small wake-up call of three days in the hospital, but I see nothing in the way of true spiritual surrender. So I spend my time living my own life (like you, in my office/half of the house), I go to Alanon, read, exercise, and I pray for God's will for me.
So, I would say definitely go to Alanon, and keep posting here. All your questions will become clearer in time as to what you need to do for you and your little daughters.
Welcome!