The thing is that even with catastrophic global warming, earth would still be tons more habitable than Mars. Any structure that could allow survival on Mars would also allow survival on this hypothetical future earth.

We either fix it or we are screwed. So we are probably screwed. Anyone seeking to build a Mars colony as an “escape” would probably fare better building similar stuff in earth deserts, or something somewhat different underwater. Still not the most sane places to go for, but more sane than Mars if the goal is “most survivability”.