Sure, my point was only the idea of a Mars colony surviving with 0 resources from Earth.

Of course I understand that, only the example with the gamma ray burst is not really useful here.

Well, one point I didn't make here but that made me pick that example is that, with the exception of a gamma ray burst, there is no tragedy that could realistically affect the Earth in such a way as to make it even CLOSE to how uninhabitable Mars is.

Global warming, nuclear winter, asteroid hit, massive solar flare, supervolcano, plate tectonics - anything we care to imagine will leave the Earth much closer to being habitable than Mars.

A near supernova would also be extremely disastrous and also kill Mars. Perhaps global warming on Venus scale?

Just playing along...