Merubin asked a question over on the Turbine boards about if the forge dungeons will still be available after the lugians leave and meanbeard replied:
The dungeons will remain. However, you will not be able to turn in the Forge Essences for the same amount of XP the Lugians currently award. So, make sure you hand an Essence to one of the Lugians before the January event!
Looks like we’ll just have to find some new use for those Forge Essences, huh?
Hmmm, wonder what is coming?