I've had that happen before. I think it was in a save from someone who didn't enter the catacombs at all, and was having a problem after scrying for the human council member (opening the catacombs before scrying fixed that).
If Lanilor does not move to the back room of the Blue Boar inn when the other healers move (perhaps because he has not given you the teleporter stone yet), he gets killed when Demona show up.
Did you not free Lanilor, or do so but not enter the catacombs after that, or something?