If the planet isn't poisoned more and if workers (and the public in general) aren't killed for arbitrary reasons on a whim, ascension is canceled. 
If the planet isn't poisoned more and if workers (and the public in general) aren't killed for arbitrary reasons on a whim, ascension is canceled.
Sure it fails when there's free breathable air, a comfortable temperature, many ways to simply leave, and it's easy and cheap to ship supplies, but what if none of those things were true, and also any equipment malfunction wasn't merely inconvenient but actively life-threatening?