As mentioned in a few places, Therella doesn't always realize that Dalton gets killed at Durlag's Tower. The main bug is that Therella's dialogue is checking the wrong DV; however I also found an incorrect journal entry if Dalton is dead. One other change is that Dalton would have nothing to say if you spoke to him prior to killing the demon knight; he now says his 'stay away' line and exits dialogue until you kill the demon knight.
A couple of folks in the open forum have talked about Dalton's corpse, but no such item exists in BG/BGEE.
APPEND dalton IF ~True()~ THEN BEGIN DeathKnightNotDead SAY #22697 IF ~~ THEN EXIT END END REPLACE_TRIGGER_TEXT ~therel~ ~Dead("Daltan")~ ~Dead("Dalton")~ // fix DV check ALTER_TRANS therel BEGIN 15 END BEGIN 0 END BEGIN ~SOLVED_JOURNAL~ ~#26111~ END