I'm asking, what if treatment fails to work...?
Then, I suppose, he will have to access the seriousness of the condition. Most psycopaths do have "normal" lives, that is, they are not up to physically harm anyone. They just don't feel guilt cheating on people, lying to harm someone they don't like or to grow in the company and so on.
In that case, if the person is seeking help, it must probably be either founded on vested interests (they see no problem in that), and the priest must be on his guard, or they have honest intellectual curiosity which will *never* revert to moral attitudes lest a miracle healing happens and I put the healing of a psychopath right up there with resurrection miracles. So the priest must think on protecting himself and protecting his flock. If it is just intellectual curiosity, the person will simple stop asking after some time and disappear. Maybe the person is just trying to mingle, even if not for a bad cause, but the person *will* hurt other people for a true psychopath simply does not understand other people's pain.
In my opinion, if the person refuses treatment and doesn't go away of his/her own accord, the priest will really have to ponder if he should allow this person to stay in the community.