Great post about what DBing is really about. You definitely seem to get it, but you don't seem to be applying it to a big part of your life.
You wrote: "Things were better so I tried to engage her but it just didn't work, so I pretty much ignored her and went on autopilot in our life, as she did. Busy with work and kids' activities, it was easy. Then, of course, the same old fights returned. " You explain how she isn't part of your life. You state clearly that you are being totally passive at this point. You are letting your M die.
So, while you have made great strides in other parts of your life, you have not changed how you react and interact with your significant other. You will continue to have those same old fight with anyone you are with until you change yourself. Trust me. My old MC told me that and it is very, very, very true. Changing partners doesn't change the issues until the old issues are dealt with.
SOOOOOO, you may as well try to work out a new way to live and interact with a significant other while W is still around. While you have CLEARLY made great strides in terms of your personal strength and happiness, it doesn't seem that you've done much work on the R stuff. Why waste the opportunity to work through some of it??? You may very well not save your M. But, you WILL have completed some important work that you need to do in any case. May as well start getting it out of the way :-)
From your brief comments here, you seem to be being passive aggressive, part of which is being very withholding. I can't imagine why W would change her mind under such circumstances. And resorting to being passive aggressive as a coping mechanism will damn any future Rs. Sooooo, again, maybe time to work on your actions/choices now. You can't have the same old fights, you can't have the same old R, if YOU change.
Now, I agree, that you changing won't magically fix your M, but maybe it gives it a chance. More important, as you recognize, it will help you be a happier, stronger, more complete person. That is what really matters.
I don't get the "I'll spend my summer living in an uncomfortable situation, resenting a lot of it, and do nothing but watch the last tendrils of my M wither and die," attitude. What is this doing for you? Why do you want to do things like that? I don't mean these as rhetorical questions, I really am not getting it.
If you are convinced that W will file in the Fall, then why don't you simply file now? Why treat yourself with such little compassion or respect? Why not set some self-respecting boundaries? Why not tell her you love her? Why not shake things up? "W, I love you and I'd like our M to work. But, this M death watch doesn't work for me. I'm planning to file sooner rather than later, though I'd love to instead take your to Retrouvaille. For your sake, for my sake, for our sake, for the kids, I'd be up for seeing if that gets us to a different place. But, the M death watch just isn't for me. I want out or movement toward exploring whether we could have a great, vibrant, fulfilling passionate M that really works for us both."
Have you read PM by the way? If not, I think it would be a HUGE helpful book for you, regardless of what you do with W or want from W or what happens to your M. It is one of those books that is about making YOU a more complete person and therefore a better romantic partner capable of much deeper intimacy and greater compassion. Good stuff no matter what. Maybe read it and then see what you think about your current passive M death watch?
It isn't a breezy read like 5LL and it is much denser than DB, but I think you'd find it to be very useful stuff.
And, finally, and probably most important, join a band