During the climb, there is a rope dangling from the harness of the climber. Usually, they clip it to the things in the rock as they ascend. There are times when they clip the rope to the metal bolts fitted to the wall. Other times, in the absence of bolts, they put aluminum devices and fixes known as protection into the cracks as they go up.
Both methods are secure and capable of bearing the weight of a car. They are designed and tested by intelligent people with degrees in engineering. If in case they fall while ascending above their last clip, they fall twice the distance between them and the clip and a little more for the stretch of the rope.
The rope stretch gets most of the force. This means that the load on the protection or on the bolt is not that substantial. In reality, the higher the climber is above the ground, the more the rope can extend, the safer it is for them to fall.