Remember in the S76 you don't have a 30 minute MGB run dry capability. If you have confirmed loss of MGB PRESS you need to get low and find a place to land as soon as possible. If abnormal noise and/or vibration you need to land immediately, the gear box might only last a minute or two. If you see the TQ rising to maintain NR (even near flat pitch) you might only have less than a minute to get it down. Once the engines are maxed out the NR will start decreasing rapidly, you now only have a few seconds to land it. Do not autorotate at any stage of this malfunction, you must keep power going into the MGB to keep it turning.
Obviously I'm not speculating what might have happened in the Bristow instance.