The vacuum lets you travel much faster, potentially much faster than planes.
The problem isn't keeping the vacuum, it's making the whole thing safe and relatively cheap at the same time.
It seems like it's almost impossible to do that above ground with thermal expansion issues and very easy terrorism. But doing it in a tunnel solves some problems. The evacuation is still a big problem.
(note that the hyperloop will be a significantly higher vacuum. There would actually be little point in depressurizing a pipe to the level shown in the video. I hear this was done on mythbusters as well)
I think you'll agree after seeing the video: attempts to let people get out of that ... there's just no point. They'll be folded into an accordion before you can say cappuccino. Literally. Failures will propagate along such a pipe at close to the speed of sound. You wouldn't get through the first "c" of cappuccino.
You should restate the problem: the problem is the same as with trailer vs car crashes: pulling the various flattened and crushed together pieces of different people apart in a way that you'd be reasonably certain the right liter of goop recovered goes into the right casket, ideally with as little pieces of the pipe in there with them as possible.
An extra issue is that every way you might recover also fails given the forces involved. Let's say you let air in ? Well that's going to form a wall of air that'll hit with a speed, force and acceleration that is guaranteed to kill every passenger, just from the acceleration. More likely that too will fold them into an accordion.
This problem is like attempting to keep a plane intact during a crash. It can't be done, and even if you should succeed, there's no point: everyone inside will be dead from the acceleration.
The problem isn't keeping the vacuum, it's making the whole thing safe and relatively cheap at the same time.
It seems like it's almost impossible to do that above ground with thermal expansion issues and very easy terrorism. But doing it in a tunnel solves some problems. The evacuation is still a big problem.