I'm one of those who would kill to hear his W say she would go to MC to try to work on he M. I don't think her saying that would cause me to have any confidence that our M would be saved, but it would be a CHANCE, which is more than I have right now.
As long as you can handle it, what do you have to lose by returning to MC? If she is simply seeking validation for her desire to D you, you can shut the MC down. But if she is truly interested, well, who knows.
For me, I wanted to continue trying to improve myself and do everything I could to be a better husband and father. In the end, I wanted to be able to tell my kids (one day) I did everything I could to try to save the M. And I feel like I could tell them that.
Another thing I learned is that if I made several changes in me, for me, and none of them had any impact upon my W, then I have a lot less to do with the cause of her unhappiness than I first thought.