the best plan is one that doesn't rely in any way on the alcoholic. if you rely on him, in any way, it opens the door for him to manipulate you. best to make your plans with your friends independent of whatever he does.
consider not keeping the divorce a secret anymore. i understand this means telling the children. he is keeping you hostage with this secret. i would blow his cover. then you can be yourself and stop pretending. it will also put pressure on him to do the right thing if everyone knows about it.
the disease of alcoholism lives in the shadows. no one is to talk about it and the whole family hides it. this causes a lot of psychological damage to everyone involved in the lie.