My oldest sister's husband was an alcoholic, drug addict, and very abusive. She left him while pregnant with their second child. My parents were overjoyed and helped her out emotionally and financially. After the baby was born, she took him back and our father gave her the "him or us" ultimatum. She chose him. For a few months, our mother would drop off food and stuff for the kids on her doorstep. One day when she stopped, the place was empty and they were gone. For the next 8 years, we had no idea where they were or how they were. Their pictures remained up in our parent's home and we talked about them occasionally, especially on holidays. At one point my mother tried to find some information on their whereabouts, but this was before the internet, and found nothing. On a few bigger events, our sister's wedding, our grandfather's funeral, the whole extended family was very sad that she wasn't there and didn't even know about it.
On the other side of the story, my sister and her family had moved to a small community several hours from us. She was trying to support herself, her husband, and 3 small children. When she was pregnant again, they had no money for a doctor. She was going to deliver at home. When the time came, the husband was passed out, so she delivered the baby herself with complications. She almost bled to death. While recovering she decided to kick him out. The next 2 years were very hard on her. He continually threatened violence and she was increasingly depressed that her family had "abandoned" her. At Christmas, she just cried all day.
A very good friend of hers told her that she should try to contact us, the worst that could happen is that she would know for sure that she had lost her family. She was too scared for a direct approach so she wrote a letter to our grandmother asking what she thought and for current addresses. Grandma encouraged her and she sent a letter to our sister. I will never forget our sister calling one night and crying "I got a letter, I got a letter!" Both our parents and I were on extension phones as she read it. It was only time I ever saw my father cry. The next day we all wrote her back. She received all of the letters on the same day and was overwhelmed. She set up a weekend to come visit. When she came, she was amazed that her picture was still hanging on the wall. We all accepted her back without question. We have been close ever since.
In hindsight. the ultimatum was the worst possible thing we could have done. I'm just grateful that she had the courage to get the help she needed and came back to us.