This could ruin your whole day ...

Perhaps we should start to listen to the Tesla guy and put some of our eggs in another basket (make sure the video captions are on - box on bottom right, left of settings; and you can lose the audio ).

If you followed the link you may never think about Excel spreadsheets the same way again.

Putting the 'one million people on Mars' to one side, here are some other options:

• long-duration refuge sites buried deep inside the mountains; 
• a (largely) self-sustaining lunar colony;
• asteroid or orbital habitats. 

They're all hard - but then, so is Mars. Any place where we need advanced technology to survive at all is going to be vulnerable to system crashes. All the proposed refuges need advanced, not basic technology, sustained by hi-tech societies and lots of skilled people.

I would much prefer self-maintaining and self-reproducing technologies (aka 'life') which could be engineered to thrive in these hard environments and could create an ecology in which even underskilled and numerically-depleted humans could survive and progress.

Maybe needs a similar reworking of human, though (see this post).