So for those who had issues trying to turn in this quest because the NPC won't appear even after abandoning/retaking the quest--
I submitted a ticket twice to get this resolved, and received this reply from the GM:
"Checking into this it looks like what had happened is you had started up this questline on two characters, but because it can only be completed once on your account this had caused the turn-in to no longer be available on Rousse. Additionally you managed to complete the quests after it so you're past the point where it would had been available to complete.
That said I have gone ahead and marked it as completed for you so the next time you login it should no longer appear in your quest log or map."
If you can, I would suggest try completing it on another character you remember starting it with. If not possible, try submitting a ticket (this will be bit of a hassle because they don't make it easy). I did have to resubmit the ticket because they tried to redirect me, so it may take a few tries. Hopefully in the future they fix the quest so this won't happen.