Ultimately, if something does go wrong, drones fail in a safe and controlled manner, for example by deploying a parachute for a safe and gentle touch-down. The University of Southampton is working closely with a spin off company developing a state of the art architecture that further increases the integrity of the onboard electronics to improve the safety of drones.
As technology improves, the reliability of drones as well as the number of safety features on board is also increasing; many drones can autonomously avoid obstacles using a variety of onboard sensor arrays. In most cases higher degrees of autonomy improve the safety of drones.
For example, most autonomous drones that lose the signal from the operator can be programmed to automatically return to their launch site, whereas drones with lower degree of autonomy would not know their location and may not be able to land in a safe area.
Broadly, the greater awareness of its environment a drone has, the more possible courses of action it has at its disposal in the event of a failure. Some state of the art research drones can pick safe emergency landing areas, such as empty fields, from the air.