It's my understanding he does not HAVE to attend unless he receives a summons or subpeona. They may try to take a deposition where he lives, but he is not required unless he receives a subpeona for that.

How common is this requirement in a civil case?

If I were him I would call the team back, refuse to go, and tell them he would not make a good witness because he does not have good thoughts toward the pastor right now...that might be enough to get the lawyers out of his face.

Life may not be the party we hoped for, but while we are here we might as well dance!