Humanity will still (probably) survive after a super-volcano eruption, but current technology and civilization is much less likely to. And once those are gone, they can never be rebuilt, because all of the necessary resources (minerals etc) needed to rebuild have already been used up, and those remaining are impossible to access without already possessing those technologies.

Having self-sustaining colonies off-planet means that technology and civilization can still survive, and be reintroduced afterwards. Getting them to the point of being self-sustaining, and having their own space-based manufacturing isn't a trivial task, but is very achievable within a century or so.