Earlier I joined one that was stuck in the Hulker room. We beat them and the door wouldn't open. We had to kill ourselves since /extract wouldn't work. Beat the Hulkers again and the door still wouldn't open.
EGO - 5900
PC-NA Character Name - Dod, Account Name - ironcladtrash
Perhaps making a purchase from the cash shop would solve your problem.
The easiest way to beat him is ground pounders. As soon as you break the first three turrets and he teleports, your whole team should shoot ground ponder stickies up on the center of the rooftop, where he floats up towards. If your entire team throws down a damage spike and detonates it will kill him instantly or leave him with less then a quater of health left.
If you don't beat him the first time it's definitely best to restart the entire map.