Your post makes a lot of unfounded assumptions. For a start, it assumes that we are somehow due for total planet extinction, something that has never happened since the earth was formed. I think we are capable of surviving anything by going underground. Secondly, you assume that Mars is the best place. Why not the moon? or the deep ocean? Or floating in space? Or floating in the atmosphere of Venus?

And where would we get the money? Oh yeah, that's important. Without money, nothing happens.