I feel late to the party with so many comments, but just thought I'd throw my own experience in for what it's worth. I agree that there is no one-size-fits all MLC and there is no predicting which way it will go, just as it is so hard to know why some people navigate midlife and FOO issues without destroying their families and others can't escape MLC and do just that. FWIW, I read Jim Conway's book (and this is going back several pages of posts) several times after BD. I found it extremely helpful. However, in retrospect, I don't personally believe he had a full-blown MLC but more of a transition. He managed to hold on to his faith and his family, which belies a full MLC, in my opinion.
I had a wallower for years. He didn't leave the house for a very long time. He was mean, cold, very, very distant. He did totally destroy our family, even though he was still here. He finally left and honestly, I finally truly started to heal then. He's been out a couple of years and it didn't cause too much separation for us to ever have a relationship. Our relationship now is better than it has been in a decade. I hear from him all the time and we are definitely rebuilding a relationship, even if not a husband/wife one yet. I can depend on him again in just about everything. He is very involved with the kids (and was not while he was in the house). He is tying up the loose ends of his MLC, I believe.
When I first started posting on this forum at its beginning, I remember the phrase that was sometimes used - "they have to leave to come back." Maybe this is true in my case. We will see. It certainly is the case for others. I truly don't believe it makes a difference or not if they leave or stay.
But all that to say that every MLCer is different even though so much is eerily the same - same script, etc.