The prospect for building a self sustaining colony on Mars in the foreseeable future is essentially zero. And even the largest disasters on earth are unlikely t

The prospect for building a self sustaining colony on Mars in the foreseeable future is essentially zero. And even the largest disasters on earth are unlikely to kill quite everyone. So the most likely outcome of a metaphorical or literal asteroid hit on Earth is that it would still leave thousands, millions, or billions of survivors on Earth, while leaving it unable and/or unwilling to sustain maintenance missions to Mars, so the Mars colonists would starve or otherwise die slowly, despite being technically unaffected by the original disaster.