If and when the D discussion comes up, tell her something like this, "As you know W, I do not want a D. I will not help you do something that I do not agree with, however I will not stand in your way." Simple and straight to the point.
As for telling your children, why would you own the demise of your M by apologizing to them? You are making changes to improve your life and your M. You will not be giving yourself a better chance to reconcile by doing this. I believe you would he doing the opposite by enabling your W. The demise of your M is not all on you and you shouldn't bear the entire burden. She wants a D. Let her own it and deal with the consequences.
Also, you probably have more time to DB than you think. Just because a D is filed, doesn't mean it is over. Not sure how long it takes to get processed in your state, but it takes a minimum of 6 months and 1 day here in California.
Keep DB'ing your tail off and don't allow fear to paralyze you.
Me:45 ExW:48 M:04/97 3 Bombs & 2 ReCons 1st BD 11/10 D Finalized 4/20 D-16 S-14 Going in one more round when you don't think you can. That's what makes all the difference in life.~Rocky Balboa