Withdrawal is one of Conway's stages, which if memory serves are aligned with Kubler-Ross' stages of grief (though I may not remember that correctly). I prefer the terms for stages of Separation, Liminality and Reintegration.
I don't have an opinion one way or the other about the possibility of OW (or OM) withdrawal. It's a term that I mostly saw HB use and haven't read much about it. I do think the OW/OM relationship can survive into Liminality, but like RCR's article says.....the nature of the relationship changes. I am seeing this firsthand in my friend's situation.
Now with that said, I don't think any LBS can tell for many months afterward when the MLCer has potentially progressed to another stage. In my friend's situation, his ex-wife started talking about wanting to return more than 6 months after expressing embarassment and shame for her behavior.