What happens when a quadrotor loses power a few thousand feet in the air and plummets back to Earth? I have no idea. You probably have no idea. But someone has a very, very good idea, because they've done some experimenting. RcTestFlight built a quadrotor, slapped a camera on it, sent it up to over 4,000 feet (1,220 meters), and then cut the motors just to see how it fared.
Quadcopters, like anything else, tend to fall like rocks when they lose power in the air. Unlike rocks, however, they have props, but this isn't necessarily going to save them. When unpowered and falling, the props spin in the opposite direction as they're supposed to, which does sometimes add a bit of lift and stability (this is good), but can also prevent the motors from being restarted (this is bad). And larger props seem to offer greater lift at the expense of passive stability. I love the idea of those passive flaps, but what I really love is that some guy just decided that he'd figure out what happened to quadcopters in free fall, and then went out and actually did it. We salute you, Mr. RcTestFlight guy. Well done.
Also, we should mention that doing this is almost definitely illegal in the United States, since you're not supposed to exceed 400 feet (122 meters) with a quadcopter. So if you try this, be safe and don't get caught. And then send us video.