You do realize that Martians abandon Mars because the protomolecule opens up worlds that are already habitable, so terra forming becomes pointless? It has nothing to do with infrastructure or economy, Mars is supposed to be an eventual second home, not a place to mine. They leave because interstellar travel becomes a reality before Mars becomes viable.

Unless we discover that Charon is actually a Mass Relay, Mars is the best possible second place for humans.

Titan is too cold and the atmosphere would require a full changeover, and the Galilean moons are constantly bombarded with radiation, Venus could support a floating colony but thats tenuous at best. Mars is basically it, if we can develop the tech to turn it into a reasonable place to be.