Yep, it happens all the time. I went on a date Friday with a woman who left her husband 5 years ago. They tried MC but in the end she knew it wasn't going to work and she couldn't explain why (she initiated the D and they had small kids at the time). Something happened after they had kids. She said she has dated guys (1 for a year), has not introduced anyone to their children, they still live close by to each other and are best friends. For whatever reason though it appears she still has no interest in being with him.
Maybe she married him for the financial security and knew he would be a good, stable man to have children with but after the children were born and of a certain age she no longer needed him and moved on to what she thinks are greener pastures.
TBH I don't think there is any way an LBS could ever predict or know something like this would ever occur. You can get into the whole Alpha Male/Beta Male discussion but I know some Alpha males that have been on the short end of the stick as well. Beta males that have been married for 30 plus years and real shitty husbands that are still married who have no business being married.
That's why I just keep reminding myself that this is more about them and what they are going through.