Have you checked the wall to the right of the locked gate?
Ok, my memory of the Reaver Citadel is hazy at best so forgive if I do beat a dead horse, but... there are two locked gates, lower and upper.
I retook the same quest you retook because of the Library Fires mess. I also thought at first that I could not get back to the questgiver as the upper gate was locked...only, like the lower gate, it could be bypassed by a breach in the wall. The questgiver was at the "forcefield" gate up the stairs.