I would expect the result to be the same as running into anything else: drone and any payload crash into the ground.
Drones are lightweight, they're not going to do much to heavy machinery. Basically the same as a brick wall.
The real fear is propellers hitting a human. The result is not good at all.
I expect some kind of automatic drone parachute system to develop.
They weigh 80-85lbs and travel at speeds of around 50mph.
The impact would be quite serious, if they crash at speed but even falling on a car or a human would be quite serious, possibly deadly, even if the propellers don't spin.
Also drone and payload falling to the ground from any kind of height could cause serious injury or death if it falls on someone.