I'm no lawyer, and I don't play one on TV. It seems to me that the church was built and maintained with the funds tithed and donated by the parishoners. The parishoners didn't leave the Episcopal church. The Episcopal Church left them, and created their own belief system. They are Episcopal in name only.
I personaly think you could make a case that the dioceses and national church have been acting in worse than bad faith for 40 years or more -- ever since Bp Pike wasn't deposed. But I can see trying to haul that through the courts ... A lot of lawyers would get rich.