My sister chose to go NC with us, her siblings, when she and her husband estranged from our parents. Ironically, I had told my parents expressly that I wouldn't be taking sides or acting as a mediator (they agreed that this wasn't my role), and I had never indicated to her that I was on anyone's "side" or wanted an explanation as to what had happened.
My AIL threw a wobbly when she found out that Hubby (an adult) had been contacting her ex-husband on occasion. She felt that because they had divorced, anybody in the family choosing to contact him was a personal betrayal of her. Consequently she became Aunt Who We Don't See. We have maintained a positive relationship with UIL and have visited his family. We found him and his new wife to be charming, gracious hosts, and their children are lovely.