I have a relative whose wife, while she was in her late 30s, had an accident and ended up in a coma. She also had a car crash in her early 20s, was in a coma, woke up, and relatively recovered at that time.
For her second coma, the doctors were initially cautiously optimistic that she would pull through, but she ended up getting worse. After about 6 or 7 weeks, my relative was ready to pull the plug, so to speak, as his wife wasn't getting better and complications kept arising. Her parents wanted to keep going because she had recovered from the earlier coma and thought that miracles strike twice.
I was worried it was going to turn into a Terri Schiavo situation, but they waited another week or two, and the parents finally were willing to accept that their daughter wasn't going to make a second miracle comeback, and agreed to stop life support.
My relative and his family and her parents are civil to each other for the kids' sakes, but I don't think they do too many get togethers.