why would they go back to church?
After all they been through they had no help from god whatsoever, to temporarly stop the demon there was a sacrifice needed by a regular human, and meanwhile giving in what the demon wanted ( a soul).
So at the end of the movie giving praise to something ( and if he enjoys it its a sadistic bastard)that didnt help and didnt even care when they were in serious trouble seems a little naiv and stupid.
And on a other note, they critise the cult for killing lives and suicide but at the same time they say that god honors suicide as a sacrifice ; that is doing the same what a cult does right.