Self-sufficiency is a bit of a sliding scale. You can be self sufficient as a band of hunter gatherers at only a dozen people but technological civilization certainly takes a lot more than that, there's more total knowledge involved so it has to be spread out over many heads and spread redundantly so that a single death doesn't remove a technology.
One can imagine a Mars that's been terraformed and grown to a population of 1 billion people in the very distant future. But at that point I expect most of the mechanism of technological civilization to live inside AIs rather than human heads.
If you imagine a colony of just 1 million people on Mars that's pretty doable in the medium term. But it's only a very narrow range of disasters that would reduce Earth's population to less than a million and not also spill over to wipe out Mars's more fragile civilization as well.
One can imagine a Mars that's been terraformed and grown to a population of 1 billion people in the very distant future. But at that point I expect most of the mechanism of technological civilization to live inside AIs rather than human heads.
If you imagine a colony of just 1 million people on Mars that's pretty doable in the medium term. But it's only a very narrow range of disasters that would reduce Earth's population to less than a million and not also spill over to wipe out Mars's more fragile civilization as well.