Terraforming Earth is FAR more likely than terraforming Mars. There is no planet B, except in wishful thinking. It would be a mistake, but I see the possibility of losing most of our life-support system and still having a handful of sapiens survive and try to squeak by, as happened before.

Of course, without air, food, or water, we die, but losing ALL of it is not necessarily all at once, or inevitable. We watch it go, and act.

A horrible life, in cool caves, with canned food until something lives to sustain biodiversity would be a sad choice. Let’s not let it happen