They might be bots. A bunch of times on the lowest three dungeons, I had tanks who simply wouldn't say a word, and just auto attack. Despite how much we talked there would be no response. Then we noticed certain behaviors which confirmed our doubts. They cure at a certain %, would visit every single room in the map. We ended up locking at least one out of the boss room and three manned it. Don't feel bad.. Really, if that person is behaving too strangely and being unresponsive its very likely he isnt even human lol.