The drone’s blades would likely still be spinning during a parachute descent... albeit at lower revolutions per minute. I’d imagine drones operate like a helicopter: in the event of an engine failure, the helicopter goes into “autorotation” in which the now unpowered rotor blades move due to the air going through the blades as the helicopter descends, thus braking the fall. However, if drones have locking rotors, then in that case the blades would not be rotating during a parachute descent.

Regardless of whether the blades are locked or spinning at lower RPMs, still better than powered drones falling from the sky!