A and B are solid, sensible suggestions. Inevitably someone stupid (possibly multiple someones, possibly in positions of power) will ignore them. We can leave

A and B are solid, sensible suggestions. Inevitably someone stupid (possibly multiple someones, possibly in positions of power) will ignore them. We can leave that to one side. With C, we're well into "what do the safeties look like" because the assumption that you can manoeuvre at all after something Unexpected And Exciting happens is possibly rash. I don't trust that designs like this one have much unpowered lift or even that much flight control at all in a power-out state. And remember too that the whole point of these things is that they're flying over presumably dense areas. The idea that there will be somewhere safe to manoeuvre to in the seconds you may or may not have is definitely on the optimistic side. But still, even given all that, a parachute should go a long way to being a workable "emergency stop" equivalent. There are failure states which it doesn't help with (for instance: a birdstrike goes badly enough wrong that a short-circuit starts a lithium fire which, thanks to our parachute, slowly drifts an incendiary path across entire city blocks) but in general I'd expect the benefits to outweigh the risks.