People die in aircraft crashes because they cant undo their seatbelts to evacuate. They panic and revert to trying to release a normal car seat belt mechanism, something they are more familiar with. That is why undoing the seat belt is in the safety demo.
So in this case, it would have been next to impossible for the pax to release themselves from their harness. In the cold, wet, dark, in full panic mode, hands shaking, they would have to 1. Remember they are harnessed to the helo, and not a normal seat belt. 2. understand that to escape they would have to cut themselves out, by locating their knife and then locating their tether, and then actually cut through the cable. Forget it. They should have had quick release harnesses like on a parachute. How did the FAA sign off this?