Sorry to hear of the pickle you guys are in. I hope you're finding this board helpful, I know I have.
I definitely advise against MC while your W feels the way she does now. It won't help.
My W told me she'd only do it because "isn't that what you're supposed to do", and "I want everyone to think I gave it a try".
In a single session with W alone, C told W that she sees people older than W who wish they would have jumped ship back when they were W's age!
She then told me to ask W if she wants to work on the M or work on an amicable D! What? I already know the answer to that question, why would I ask it?!!
I fired her and thankfully W never expressed a desire to go back. That was a year ago, were still together and I still have hope.
M: A really long time. Crisis: 5 years. She's still worth it.
Life is never made unbearable by circumstances, but only by lack of meaning and purpose. -Viktor Frankl