i think as long as you haven't actually gone into the area with aribeth to make the cure, you can do whatever you want... like finish up quests.
but then again, i've never tried that before. i don't believe you need aribeth for the Tomb of Neverwinter quest... just the judge, so give it a go. most that can happen is that you won't be able to. but then you can always go back to an earlier save before you turn in the last critter.
many variables can and DO corrupt easily in the savegames, as i've seen numerous times on the official forums, so i know, as a good rpger, you're making lotsa separate saves, right?
V***V