I am currently separated from my AH, and I have recently decided that I will be filing for divorce. I will try to answer your questions from my own experience.
When I moved out in October, I made the conscious decision to not use it as a threat, an ultimatum, or a manipulation. I decided that I could no longer live in a toxic environment with an active alcoholic who had no intention of changing. So, I did not really have any expectation about what AH would do when I left.
Before I left, I did a lot of advanced planning. I didn't want my leaving to be the result of one particular fight; rather, I wanted my leaving to be a conscious choice to change an intolerable situation. Fortunately for me, AH and I were always pretty much financially separate, so I already had my own accounts. I leased an apartment ahead of time so I had someplace to go. I timed the actual move for when my parents were in town so that they could help me, and I didn't have to do the actual move alone. I also hired movers so that I could go quickly and all at once.
I did not tell AH in advance that I was planning to leave because I did not know what his reaction was going to be. I didn't want to create a situation where I was forced to go to a hotel, or where I was afraid to get my things. So, the morning I had planned to leave, I had my parents waiting outside, and I told AH that I was moving out because I did not want to live with his drinking any more. He was shocked (as I knew he would be--he never wanted to acknowledge that his drinking was a problem), and tried to get me to stay. I told him simply that nothing he could possibly say in the next few minutes would change my mind. I also told him that I hoped he would get help, but that was up to him, and that I hoped he would come up with a plan. I told him that I hadn't made any decisions with respect to divorce, but that I needed to remove myself from the situation. After that conversation, I had backup with my parents and the movers, and I was able to get my stuff without incident.
After I left, I had several conversations with AH, who, to my total surprise, actually started going to AA. However, I recently went no contact with him because I felt like he was constantly manipulating me by trying to figure out what I wanted to hear, rather than really embracing recovery. I truly hope that he does figure it out, but I just can't deal with talking to him about it all the time.
The thing about AH supposedly getting sober is that there is a ton of mistrust, and no matter what, it's all about him. Even if he is serious, recovery is intensive, and it's all focused on him. If he's not serious, then it's a total waste of time because I can't live with an active A anymore. I have discovered that there is simply no room for me in the relationship even if AH is serious about recovery. So, I am done.
Fortunately, we don't have kids, so that was not an issue for me. It has taken me a few months to come to a decision to divorce, but the thought of going back to that life makes me physically ill. And when I left, I was already so physically unhealthy--couldn't eat, couldn't sleep, couldn't relax. So, I took back my life, and I think it's the best decision I could have made.
The absolute hardest part of the separation/move was the actual moment of telling AH. I would never want to repeat that experience, but I'm glad I did it, and I got through it. That also keeps me from going back inasmuch as I don't know if I have the strength to go through the act of leaving a second time. So, I have decided to not put myself in that situation again.
I'm sorry you are going through this, and I wish you luck, wisdom, and courage! It is agonizing for sure, but I had 2 things that motivated me. One, I kept thinking about the fact that I didn't want to waste my life in a horrible situation that I did not have the power to change. And two, I did not want to become someone I didn't like. I could feel the toxic environment changing me, and I didn't like what I saw. Just remember that it IS okay to make this decision for you, NOT HIM.