We don’t know how fragile technological civilisations are because we’ve only got one example. It’s reasonable to say the technological civilisations are highly specialised, and it’s not unreasonable to suggest that excessive specialisation is fragile as we have many examples of that in the form of biological speciation.

However, the economic cost of making an interstellar colonisation ship is so vast, that from where we are it seems reasonable to assume that anyone who does it has fully automated manufacturing and resource gathering – or, to put it another way, they are post-scarcity. If you’re post-scarcity, then you’re no longer fragile, because you can have a complete backup of everything you need, including the skills needed to rebuild.

Of course, there’s lots of ways for things to go wrong, and if I were to imagine badly written control software that means the fully automated manufacturing kills everyone, I’d be accused of being too derivative rather than implausible…