I warn them about self destructive choices made on impulse, like drinking too much, spending a bunch of money, or hooking up with someone else. A poorly thought through decision made out of hurt or anger can do a lot more damage and just make things worse. I let them know they'll have to decide how long they want to wait to see if she'll change her mind. My motto with this situation, as with many others, is "Hope for the best. Plan for the worst."
I tell them that, once again, they need to listen to what she's saying. I encourage them to be humble and take responsibility for not listening or taking her seriously. I encourage them not to defend themselves or make excuses. I remind them that actions speak louder than words but warn them to choose their actions carefully. I remind them that chasing will just make her run further faster, and could result in restraining orders or other legal problems if they start being a "creepy stalker."
I tell them to make clear that they love her and want things to be different, that they're committed to changing, and then to back off. I suggest that they let her call or text if she decides she wants to. If they have to make contact to talk about kids or legal matters, or just can't not text or not call at all, I suggest they don't do so more than a couple times a week. I say keep it light and brief.
In future conversations, or when they have to see each other to exchange the kids or paperwork or whatever, I advise them to be nice and look nice. The "I'm so upset about you I haven't showered or changed clothes in a week" look is probably not going to score any points. I suggest that they avoid pushing for conversations about working things out, and that they avoid being mopey or whiney. No "poor me" FaceBook status updates or tweets. No clips of sad love songs for her to hear if she calls the cell phone.
I suggest that these men work on changes they want to make for themselves and get involved in meaningful activities so they aren't just sitting around being sad. If they really do want to start going to church or counseling, I encourage them to do those things. If they really do want to spend more time with their kids, I encourage them to do so. I warn them to do these things because they really do want to, not just because they hope their wife/girlfriend will notice and come running back. I tell them that may or may not happen, and if they're doing things for that reason, they'll just quit when things don't go their way and come across as insincere.
If she starts thawing a little, I let them know to take it very slow. She'll have to really see that he is different. Trust has to be reearned. Some couples do get back together and go on to have a healthy fulfilling relationship. If his wife/girlfriend shows no sign of interest or a wish to come back after several months, I let these men know they'll have to grieve the loss and try and learn all they can from the experience so they can do things differently if there is a "next time" with someone else. That's not an easy process, but its necessary to come to a place of acceptance with what is. I warn them about bitterness and hard feelings and how poisonous those can be.