Well if you think she's already on the way out and is only being nice to make D smoother, you have nothing to lose by going to Plan B. It's not like it could make things worse, right? Now I should preface all of this by saying I've never had to do a Plan B myself. I have read about lots of Plan Bs here; some were well executed, some were not. Some were astonishingly effective.
I think you're mistaken when you say Plan B will not have an effect on your W.
She's getting a lot of her ENs met by you. You engage in recreational companionship (even though it's you initiating it), she texts you when she needs something, she engages in conversation with you, she gets some sort of admiration fix by waiting around until you contact her.
In Plan B, she will get NONE of that from you. What a shock to her - finding out her little poodle isn't begging at her feet for attention! Her princes status will be upset. What a shame for her.
Another thing -- up until now, she's been calling the shots. She decides when she'll see you and talk to you, and when she won't. She decides if and when she'll move out, etc. "...if I feel like talking I will if not, I will leave."
Plan B puts you *totally* in the driver's seat. With Plan B, you clearly outline your love for her, your need to protect that love, and a clear path for her to return to the M. Then you disappear. If she wants to play, she plays by YOUR rules. What an upset to her "I own the world" mentality!
Sure, she could still decide to exit the M but she could do that with or without Plan B. I'm not totally convinced she's done, either, because she hasn't filed the papers. Even if she does have a temper tantrum and file "to show you" that's not necessarily the end. Marriages have been recovered while the D proceedings are ongoing. So this battle is not yet over.