This is addressed in section 4.

A minor depressurization of the tube is unlikely to affect Hyperloop capsules or passengers and would likely be overcome by increased vacuum pump power. Any minor tube leaks could then be repaired during standard maintenance. In the event of a large scale leak, pressure sensors located along the tube would automatically communicate with all capsules to deploy their emergency mechanical braking systems.

(The capsules would be around 6 miles apart at their top speed.)