That article seems to be referring to winged UAV drones (e.g. Predator) not the quadcopter-type drones used for deliveries.

Good catch. It is possible for quadcopter-type drones to come with four extra motors that sit opposite of the traditional four motors and props and face down with slightly different sized props and rotating the opposite way.

In the case of failure of a prop in this configuration (the most common failure in my own experience with quads and octos), it is possible to program the n-copter to automatically change to flying in 7 prop mode or 6 prop mode or 5 prop mode, and so on and so forth as a redundancy feature. This could help with a not insignificant amount of crashes but obviously comes with increased costs.

Airplanes get regular (and quite extensive) maintenance though.