[ddingus]

On what time line? NVM, I didn't see other comment. Makes sense.

Seems to me, a process capable of refreshing a livable atmosphere could just be used as needed, given a sufficiently long depletion time line.

Anyone have ideas or info on what that looks like? My mind moves to things like diverting ice from space. Big scale.

[M_Grey]

Well, to do it all at once you'd need an icy planetoid, but that's not realistic at all. More "realistic" would be a fleet of robot probes designed to steer water ice laden asteroids onto a collision course with Mars. It would be like building up water a snowflake at a time, and it would be touch to manage. If you do it before an atmosphere starts to develop, you'll lose a lot of it. If you start to do it later though, you're going to be kicking up a lot of dust, but maybe that could be put to some use.