> he believes that we must be a multi-planetary species to survive which means Earth is destined to die.
I don't read it as "destined to die", just that there is a non-trivial chance.
Mars… I want to be excited, but the more I think about it (and, bluntly, the more bad decisions Musk makes), the less I like the idea.
That said, Mars is sufficiently difficult in all the right ways that if we can make a self-sustaining colony there, the only way life on Earth will end is some kind of self-replicating swarm, either in the sense of an engineered pandemic (specifically an engineered one: a merely natural one we can probably defeat just like COVID) or a more sci-fi von Neumann swarm.
Mars has half our sunlight, it is colder than Antarctica, dryer than the Sahara, the air is thinner than the top of Everest, the soil is toxic, and we'd have to make any hydrocarbons from the air itself rather than digging them up.
Make a Mars colony work despite all of that, we'd easily survive a repeat of the asteroid-ending impact or nuclear winter here on Earth.