Does anybody else get a shudder when someone refers to a helicopter as "Chopper?"
Anyway, I believe this was investigated by the Army decades ago and moth-balled. I'm sure
Lu Z or
Rich L can elaborate more. Try contacting the folks below and see if they have any records available...
U.S. Army Aviation Safety Board
I don't believe it would be practical. There are too many variables that you would not be able to control in an uncontrollable situation. Also, the blades would need to be at zero rotation less they steel air from the canopy or get tangled in extreme attitudes.
I guess it would be practical if ship were in blow-back where the helicopter is a giant lawn dart! Also, speaking as a former Jump Master, the aerodynamics and capabilities of parabolic parachutes are limited. Too much airspeed or weight when deployed, and you will rip the gores right out of the package. If the helicopter experiences complete failure with blow-back, the kenetic energy created with mass and speed will be too great - - even for ballistic heavy drop parachute configurations.
Besides, these types of parachutes are complicated... and they don't always work! I can't tell you how many times I've seen a jeep or a tank burn in... amazing site. Small systems for LIGHT fixed wing aircraft and ultralights are successful because they don't need to be complicated and weight isn't as much a factor. What you propose is quite the opposite. Good luck!