Okay, I got all 5 relics and have followed Volgar into the last realm. Have killed all the creatures and teleported 3-4 times. Came to last gate, Volgar taunted me a bit. Sent tougher creatures out. I killed them all, but the gate won't open. I have tried the walls in case something was stuck, but no dice...gate just won't open.
My last save besides this area is a way back. Please tell me I missed something.
I believe that sometimes there are creates up high that won't come down. Or on the other side of the gate. You could also try looking for another gate (I was at the wrong gate the first time around).
I had trouble here as well, some creatures become stuck inside the wall behind thier spawn point, thankfully I was able to kill them through the wall with area affect spells.
In patch 1.3 is written - no stucking monsters --> so, which is your current patch? I experienced the same problem - creatures stucked on the top of the rocks - check carefully. Good luck!