Reviving this old thread. I can't seem to find anything on if this quest was removed or not or maybe just a bug or if I just missed it all together.
I have an add-on that shows a few "!" around town.
New in Town: Malareth has been run out of Vulkhel Guard for the time being, but she vows to return at a later date. Those of you on this quest are advised to abandon the quest until she returns. Not completing this quest will not impact any achievements.