Thanks for being so candid, it can be hard (even on the internet). I would say that you probably should not get your hopes up too high. Unfortunately your expectations have to be low since you know that your mother will never leave your father or be completely free of him. I am glad you have come to accept your mother's situation. I am not saying what she did is not wrong, I am saying that it is GOOD that you have come to understand her side of the situation. Furthermore, I am glad you were able to meet with your mother but I think you would have enjoyed it more if your father had not been in another booth. Do you think your mother would be willing to meet with you without your father present. If not, you might want to stick with emailing for now. It would probably be best to take it very slow. I think you are right when you talked about not bringing up the past since it would make her retreat. Right now, you should probably just talk about your kids and stuff like that. Even if your father passed away tomorrow, that does not guarentee that your mother will want to talk all about what happened in your childhood. I am sure she feels at least a little bit of guilt, although your father did the abusing. So in summary, don't get your hopes up, take it slow, and in the end, if you believe that you are better off without your parents, do not feel guilty about it. It is your choice and you have every right to do what is best for you.
ETA: Wow! I am amazed that you pressed charges! Good for you! It is very rare for a 15 year-old to have the huge amount of courage it takes to press charges against someone that victimized you for so long! You are a strong person.