Did you try the F11 Unlock function?
Did adding the sigil to your inventory update the quest? If the quest is still listed as unfinished, the game could be checking the quest log, rather than your inventory.
Do you at least have the other 3 subquests marked as complete?
In the room where you fought Ba'al, a couple people had the loot bag drop under the platform Ba'al comes up on at the beginning, one of whom managed to get close enough to get it through the gap between the floor and platform. Godmode and the teleport function may allow you to get under the platform, if that is where the loot bag is.
The teleport function will let you bypass the door, and seems to work as far as being able to advance. Turn into a dragon, hit F11 and then use the 'goto Region' function to get to HoE_DreamScene Main.
