Lost Quests

[Bladesbane17]

So I've been following an epic quest called Ascension for Destruction's side, and it took me Chaos Wastes, to Praag, and to the other side of Praag. I got all the way to the Tower in Cinderash Enclave PQ, when I needed to break a chaos gem or something at the top to release a demon, T'zeentch's herald. Unfortunately he despawned before I could accept the next step of the quest line, because I was a bit busy keeping alive before I could accept, (the wizards I had to kill all respawned at the same time.) Worst part is I can't resummon him. To any who's at all familiar with the quest I'm talking about, is there any way to accept the next quest part some where else?

I know this isn't the only quest that has this problem, where you have to click something to get another quest, but if you don't accept it, and something happens, you can't reclick the object to activate it.