So in playing this boss fight a bunch of times, I did die twice. Once was when none of us bothered to shoot the barrel on the train track. The other was somehow my random Helena partner could not manage to shoot the tentacle at the end (I was hanging over the edge as Ada, so couldn't start shooting right away).
For ps3 there are about 11 hours left and we need about 3k kills. Chances are its done because a lot of peoples kills don't register until after the event is complete, I think. If not, its sooo close! I think we can get it.