Having carrid out an uncountable number of winching operations in the South China Sea can I put my oar in.
Some twin-engined helicopters will fly away from a OEI situation if it is cold and windy enough. Unfortunately for most twin engined helicopters those situations are too rare. The 332L1 to the best of my memory will hover OEI OGE at about 12,500 lbs with Zero wind in the Hong Kong area, which equates to just the crew and no fuel. Things get a lot better when there is some wind.
That was me winching inside the OEI curve with 7 knots plus 5 knots from the tanker with 2,000 lbs of fuel on board at about 28.C. Add 800 lbs for mooring crew and it come to about 15,300 lbs. It could have been a lot more, the 2,000lbs just happened to be hanging about. Twenty knots or so and you were above Max weight.
THE OEI HOVER OGE IN MY CASE WAS A PUBLIC TRANSPORT REQUIREMENT.
These same wind conditions would give you flyaway whilst on SAR duties if the weights were the same. Normally when offshore there is a fair amount of wind which keeps the OEI curve well up the weight scale. When the wind drops the picture changes; judging by the weather history and the video in this case they had less than five knots.
There is a not a lot of differences in hover performance betweeen an L1 and an L2. With any sort of fuel load plus what an SAR helicopters carries they were not going to fly away. Pickling the water tank might have slowed the rate of descent but when the floats went off they will have been dragged into the water.
I would not have thought that the GFS would have worried too much about OEI flyaway. Their previous chariot, the Sikorsky S76C resembled a brick if an engine stopped in the hover so that was what they were used to.
Personally, all things being taken into consideration, they did as well as anybody could be expected to do in the circumstances.