Hence "if we had a self-sufficient Mars colony". Any initial mars colony would not be self-sufficient, but even just by economics alone that would change as the colony grows.

Even if we get stuck in the "initial colony" stage (which is not the plan of any Mars-colonization proponent) with precautions comparable to the ISS you'd still have a colony capable of surviving a minimum of four years (two launch windows, in case one delivery goes wrong) and the capability to return to Earth.

That's one more reason to start Mars missions as soon as technologies allow. It will take a long time to build a self sufficient colony on Mars.