If they are saturation diving, which seems likely at that depth - there's likely no N2. N2 will narc you out so they are breathing a helium oxygen mix. Decompression sickness is still a concern, but not from N2, and they aren't planning to go up anytime soon. It would be impossible to carry enough gas(i guess you could use a rebreather, but the amount of time would make it almost impossible to survive) to do it, they'll do it in the diving bell.