????????

Hello, the character on the final quest died DK lvl 64. I fell into the textures and couldn’t get up from my body. I used the services through my Personal Account. The character now stands in the citadel and cannot leave it NPC no quests no what to do?!

Look for anything you can interact with, NPC's and objects alike. If you really can't find anything, write and in-game ticket and explain there what happened.

Is the quest completed, or is it still in progress?

I see two options you could try: a) Find a way to quest area and find an NPC you can talk to (maybe there's a restart for the last event) or b) Abandon the quest, relog and see if that does anything, you may have to wait for next morning for server reset.