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.)
I was studying in the LW Study Hall, and during our break someone posted this link to the official hyperloop announcement:
http://www.spacex.com/sites/spacex/files/hyperloop_alpha-20130812.pdf
One member was doubtful it would get past regulations, and another said "tentative p>0.05 that a hyperloop gets made by 2100", which was met with "p>0.05 that uploading people and moving them between bodies will be available by 2100".
It struck me that people might be interested in betting on things like this, or at least having a conversation about it.
A few predictions to start: