IMO it will for sure be the straw that breaks the camel's back----especially if they're both pretty unhappy and aware that there are issues. They're both going to love the freedom, space, not having the constant tension of their differences and distance, etc., and they're going to decide they don't want to go back.
I also predict that they will both be remarried to other people within about five years and they'll both have children with their new spouse. Many times childless-by-choice people simply don't want kids and have a very healthy marital relationship, but in others cases the couple is ultimately not starting a family because they don't feel the chemistry to have that sort of tie---I suspect that's the case with these folks.
I do agree with the most part except for the part of being remarried, i am not sure about that but separating at this juncture in their relationship mite cost their marriage.
My 2 cents.