Dhuum's Release is Inevitable

[draxynnic]

Actually, it is outright stated, in the Terrorweb Queen quest:

Originally Posted by Reaper of the Spawning Pools

The source of this trouble draws near. The more we turn the tide of battle against the demons, the more desperate they become. It will not be long before a Terrorweb Queen arrives, anxious to strike down that which has destroyed so much of her brood. When she arrives, you must destroy her.

(if asked about the quest): If you can destroy the Terrorweb Queen, it should stall the demon's attack for a time. Charge forth into the heart of the demon spawning pools and see if you can draw out the Queen.

[necronium]

Why don't dervishes have an Avatar of Dhuum? Surely there are loyal servants of Dhuum that are "people", for lack of a better term. I am referring to something like Varesh Ossa, and Kahyet. Which could be a way that he gets released, although that may be a kind of rehashing of nightfall except just swapping deities.

[Konig Des Todes]

There's not a single cult of Dhuum in Tyria, and he was imprisoned prior to the very creation of Dervishes (same with Abaddon, though why there are Margonite dervishes is unknown).

Unlike Abaddon, there's been 0 evidence of Dhuum's existence in Tyria - all knowledge of him comes from the Mists. Though since Nightfall, such would probably now exist in Tyria.

[draxynnic]

Personally, I was expecting Varesh to have an Avatar of Abaddon form, and possibly Margonite dervishes as well, albeit purely as a monster skill.

Like Konig says, though, no-one in Tyria apart from the select few that were allowed to visit the realms of the gods knew of Dhuum's existence pre-Nightfall - or Menzies, for that matter. And since knowledge of a god in the material world seems to grant it power in that world (which is why the Five tried to remove references to Abaddon) it's possible that even after Nightfall the Order of Whispers tried to limit knowledge of Dhuum and Menzies.