ALso, since we'd probably at least have a few months warning, expect to see a ton of escapees from Earth descending on the Mars colony. A 1000 person colony being hit with an extra 2000 mouths to feed, many of whom won't have the right skills to be useful, would be a disaster. If the colony starts shooting at teh arriving ships, they just might shoot back, or conflit might break out among the colonists over who gets shot and who doesn't among the new arrivals.

OR who knows, in the huge social and psychological disruption of Earth being destroyed, I wouldn't be at all surprised to see fighting break out. There is no doubt the colony would have be to run a LOT differently than before the cut off from Earth -- who will make those rules, how will they be enforced, and what of those who disagree. What about general mental illness? Those colonies would be extremely vulnerable to suicide terrorism.

Again, I doubt they'd even reach the level of techological self-sufficiency in a reasonable time, but to be resilient enough to handle a social collapse and outbreaks of violence they would have to be very large, dispersed, and robust. That'll take a very long time, I think.