The partially evacuated pipe is what makes the entire system perhaps better suited to earthquake zones compared to trains.
With a train, there is no way of knowing whether both tracks are still intact short of a visual survey over the entire length of the line. Forcing all trains to stop immediately.
With the hyperloop, any breach of the pipe, will let air into the tube, which increases the atmospheric pressure and forces the pod to slow down. It's a nice passive safety system for everything running in the pipe and is really easy and cheap to monitor centrally because you just need a few pressure sensors dotted along the length of the each pipe section.
It doesn't tell you where the leak might be if there is a leak, but if you can maintain a low pressure you know the pipe is probably still intact.