Tried it with my sage today. He has 228-234 purple gear, fully augmented. Managed to kill all the imps but when I was done I noticed I was missing one of the turrets. I checked all the connection points and finally found one that I couldn't click. It was gray. So I can't complete the quest and I do not want do it again because it was a real pain. The npc's didn't help much so I died a few times while trying.

I totally agree.

When I counted, a few days ago, it looked like the hours left of double XP would last until the end of the year. But it looks like it's gone now?