Circling the drain

[cat03]

how likely is it that he will commit to working on our M?

You'll crack your skull trying to figured this one out, trying to get into his head to see what's he is thinking...don't. He is clearly on the fence and at this point this is what he has to offer, his willingness to go to C which brings us to point B:

he will not return to our M as it is right now

If he had to make the very very hard choice to leave, there is no way he wants more of the same and I don't blame him. Back in 06 when my then H left, I thought I was a fine W, I came home from work every day, cooked, cleaned, cared for kids...but I disrespected him in many other ways, I was at some degree abrasive because I thought my way was better, etc etc. It doesn't excuse the way he left, but my point is I was at fault too. So I ask you to look at yourself hard, to accept your end of the blame, it takes 2 to tangle. I also recommend reading "the proper care and feeding of Hs" by dr Laura. I was horrified to see behaviours that I thought ok were actually detrimental to my M.

Even though I'm not a prime example of a succesful D bust, for a while my then H came back after leaving for 8mths, it took him a while to realize that he also had a part in the demise of our M, at least 3mths of an anger phase in which he blamed me for it all...it was a long process so dont' hold your breath and hope he moves back next week. I DB and changed, and those changes are with me today even if he is not, I learned a lot about myself and by God's grace I'm a better person.

When I read that Cing works only when both people are committed to the M, I begin to think that I'm grasping at straws.

Your H wants to see if the M has the hopes to be repair, he does not want to D but does not want to live the same way as before again.
Before he fully commits he wants to see some change (he will, hopefully, learn that a degree of compromising is also expected from him). You can't force anyone to go to C, that'd be a waste of time. You need to take things one day at a time and see what's there vs what's not.

It's like dating each other again and going back to basics. You need to be patient and not expect things to resolve in a matter of weeks. You and him need time, gladly it seems that your MC is a good one and that she will begin by learning about each of you to get a clearer picture where the miscommunication begins, because that's the core of everyone's problems: miscommunication, muted expectations, buried hurts, etc etc.

Be confident, have faith, I see a lot of hope in your case, I will keep praying and hoping that things move in a positive direction for you both, but you have to be patient and not let fear rule your mind.