I think we need to look at the broader picture and not just focus on the affair.
An exit affair is just that: I want out of the marriage, but I'm too much of a coward to say it.
An MLC affair is a symptom of something much, much larger. Even though they spout ILYBIMILWY and divorce becomes a very real part of our lives, the MLCer seems to take one of two paths: immediate or long and drawn out.
We need to step back from the affair and look at the whole of the behavior of the MLCer. Running down a mental checklist with mine, I've seen cake eating, monstering, touch & go's, wallowing, indecision, guilt, control, shark eyes, escape and avoid--pick a symptom, and he's exhibited it. Conversely, I've a friend whose wife was probably an exit affair. She treated him like crap, but he has never seen the kind of shi!t we go through beyond the affair and an occasional sense of entitlement on her part. Could be that she's female, but I don't think so.
I don't think we can predict which ones will try to come back and which ones won't. Often, as has been said many times, the final decision is left up to the LBS. Before we are faced with that, though, we need to do the mirror work and let go of the idea that they might come back.
What does OP tell us? Live our lives as though they won't come back.
It's the best piece of advice we receive, I think. Unfortunately, it's also one that I'm not certain we can really understand in the beginning.