I think your idea to leave during the "hard drinking" portion of the party is a good one. Another possibility is to ask everyone to leave after the activities are done. They can take their hard drinking to someone else's house or a bar just as easily as they can do it at your house. Do you really want that kind of activity happening in your home now that you don't drink?
As far as your husband, it's very difficult ( if not impossible ) to explain addiction to those around us. We barely understand it ourselves. You are under no obligation to tell anyone about your drinking/not drinking - that's a personal decision you've made ( and a good one at that ) and you owe no one an explanation.