I entered the Dead Nations and everything seemed to be progressing normally until it finally came time to speak with the Silent One.
After wrapping everything else up, I accepted the quest from Hargrimm to kill cranium rats in exchange for an audience with the Silent One; I completed the quest without a problem and returned to Hargrimm, and he said the Silent One was ready to see me. At this point, all of the locked doors in the Dead Nations have opened clearing my way to leave, with the only exception being the door to the Silent One's chamber! It's still locked and his guards have no new dialogue options. I can't seem to weasel any new dialogue out of anyone else in the Dead Nations either, so I'm basically resigned to the fact that I'm not going to be able to trigger the door opening any time soon.
At best I think I'm going to have to miss out on whatever experience/gold/plotlines I should have received at this point, and at worst I fear I'll encounter a quest later on which will rely on the completion of this quest and my game will effectively break.
This is no glitch. Hargrimm doesn't grant an audience with the Silent One, you don't need an audience to ask for permission to leave any more.
The only thing neccessary for progressing is getting the doors opened clearing your way to leave which you already have done.
The only other really useful thing to do there is to learn the "Stories Bones Tell" skill to be able to talk to undead.
The rest are just little sidequests which yield little XP, not worth having spoiled your game.
