So, assuming you are a safe flier of quadcopters, you are NOT flying over people to start with. Quadcopters fail fairly straight down when they fall. RC Airplan

So, assuming you are a safe flier of quadcopters, you are NOT flying over people to start with. Quadcopters fail fairly straight down when they fall. RC Airplanes can continue flying after engine failure and possibly cross over people. Of course, both are a danger for fly-aways which would concern me a whole lot more than an engine failure.