Are there any helicopters that have a system to slow descent in the event of a gearbox or rotor failure?
There were plans for exploding bolts on main rotors followed by crew ejector seats and an airframe parachute but if you've worked on helis then you'll probably understand why these ideas were shelved, but they were tested - looong ago.
Its about the only thing I know that could slow descent in the event of catastrophic gearbox or rotor failure!