If you drop a mouse down a mineshaft it will likely have a bit of a jolt on impact, then scurry away looking for some bit of cheese. If you drop a horse down a mineshaft there will be horsebits splattered on a very large area around the point of impact. Noise problems are inherent to fast spinning rotors, gravity is where the real problems are, and redundancy in drones is more along the lines of controlled crashes than emergency landings. I'd be very much worried about the performance of the system if one or more rotors failed to do their job.

Helicopters auto-rotation is not at all comparable to a drone with one or more failed rotors, a helicopter that is autorotating is comparable to a gyrocopter, it will fly relatively well, a drone with one or more failed rotors will not fly well or even at all.