If you aren't already doing this keep a diary; dates, details, everything... about any time OM threatens your kids, or does anything that can potentially hurt them. The main thing now is to let go of W and focus on your children.
If not divorcing her gives you more control over the kids then you might consider not filing even if you never want to be with her again. Don't file for D unless you know for certain you can have full-custody.... you do not want your kids abused by OM and you should do whatever you can to avoid that.
If necessary stay in M until the youngest is of court age to determine if he or she has to go visit mom (maybe age 13 or 14? I know at some age in my state kids can go against court mandated custody and not visit with a parent if that's their choice).
I personally think whatever gives you more power in caring for the kids is what you need to do. Although if you need to protect yourself finanically you might do the research on legal separation (if it's not already a legal separation...) and see if that might be a wise way to go.
Take care of you and try not to wonder or think about W. What's done is done and let her deal with the stupid decsions she's made. Tell the kids this is an example of how you shouldn't live your life. Let them know that kids should always strive to be "better" than their parents, learn from the mistakes they see and create better lives for themselves.
There is no arriving, ever. It is all a continual becoming.
