Another reason not to confine your civilisation to one planet, or to planets generally.
Much harder to wipe out a civilisation that's dispersed among hundreds or thousands of smaller space colonies. Especially if many of those colonies are hidden in an asteroid belt of millions of rocks.
Take out Earth, Mars, and Venus for good measure.
Whatever scattered remnants that are left of humanity hanging out in the asteroid belt are going to have a hell of a time finding food to eat or oxygen to breathe.
Why?
Do you think they'll be reliant on planets for food an oxygen? That's daft — they will be growing their own food and mining their own oxygen.
Also, I doubt they will be "scattered remnants" — there's likely to eventually be a far larger population off-planet than on.
Better to strike first than gamble.