You bump into Carl/Carla whom you haven't seen for a reasonable length of time (a year or maybe several years). When you last knew them they were in a relationship with Will/Wilma.
AIBU for not knowing the correct etiquette in regards to asking how Will/Wilma is doing?
Part of me thinks it's just polite, it may even be impolite not to. The other thinks that anything could have happened with Will/Wilma in the intervening time. A very acrimonious split for instance.