IMO, you have hit upon a weak link of the SSM approach. Despite the sincere positive efforts on the part of the suffering HD partner, there simply is no guarantee that the LD partner will ever respond. None.
Rather than use the term "weak link," I would simply call it an inherently optimistic approach. Every couple and every marriage history is different, and I agree with you that there are situations where the marriage may not be salvageable, at least not in a fashion where both partners end up happy. I do, however, believe strongly that if both partners are willing to work hard to save their marriage, they will most likely be able to do so. If only one partner is putting in the effort, then the initial goal is to wake the other partner up enough to get them on board --> to break through their resistance and resentment barriers enough to rekindle some hope in both partners.
When I started my own efforts at recovering my marriage, I too started out with no guarantees that I would be able to achieve a break-through with my wife and get her to work with me. But I decided that I loved her enough, and that I valued my marriage enough to put forth every effort, even if it turned out to be all one-sided. If that had been the case, we'd be in the process of splitting our assets right now, as the school year comes to a close and it's easy to relocate the kids over the summer. However, I began to see signs of positive change within just a few weeks of hard, sincere work at winning my wife back: at least in my case, Michele and the Rosbergs' where shown to be on the right track. My wife and I are happier now than we have been in most of our 22 years together, and we have only just started walking down the path to recovery together. It's still rough for both of us sometimes, we stumble and regress now and again, but I'm confident that over the next year or so, we can be fully 'recovered,' as long as we stick with it.
I'm sorry that your own situation did not work out, MichiganMan. You're right: there are no guarantees. But just because your own situation did not work out, does not mean that others cannot succeed -- every marriage is different. And I think every marriage is worth the effort to save, even if it begins with only one partner being "big enough" (to quote Dance Queen) to step up to the plate and try.
Take care,
Bagheera
Me 50, W 45, M for 26 yrs S25, D23, S13, S10 20+ year SSM; recovery began Oct 2007