Helicopter energy
These discussions of how to best deal with a loss of power are interesting.
I suggest the reason for what seem to be substantial differences of opinion simply reflect that helicopters are more complex than fixed wing aircraft.
In a fixed wing aircraft, you can trade speed for height, adjust attitude, alter power, and perhaps deploy devices to vary lift and drag (not all independent), and that's about all.
In a helicopter, there's an additional energy store in the rotor to take into account, and a wider range of relative wind values can be experienced, vertically and in azimuth. The lift/drag on the rotor can be changed quickly, with attitude changing in response. There's a significant gyroscopic effect too, restricting acceleration and attitude.
With a three-ton helicopter, the kinetic energy in a 10-m diameter, 200-kg rotor at 200rpm (~2MJ), scales with rpm-squared and matches the kinetic energy for a forward speed v~75 knots and the potential energy gained from dropping h~200 feet. The important energy quantities involved in this case are all comparable in size, and the best way to trade them can clearly be debated.
A very plausible answer seems to require "it depends". The importance of maintaining a store of energy in the rotor is clear, but there are different ways to achieve that: exchanging height, forward speed, or by reducing rotor drag.