And you know if that does happen the children of these Terra Nova folk are going to be asking "why are we living in these shit holes when we can go top side?"
Again, check the transcript. The Enterprise
crew relocated them to another continent where it was safe to live on the surface.
The thing to remember -- and that too many Prime Directive stories forget -- is that preserving a culture does not equal keeping it unchanged. All cultures change and adapt to new circumstances all the time. So they can still be Terra Novans without living permanently in caves. They can change their way of living but build on the customs of their forebears, evolve them into something that's still distinctly their own.