How quickly would the governments of Earth get off their asses about colonizing Mars, if it's discovered that a meteor was going hit Earth and end all life on the planet in the next couple of years?
What exactly would that achieve? Mars is DEAD. Inhabitable.
If you want to build self sustaining bunkers where people are locked in anyway, you can do that on Earth as well.
Even if a meteor the size of Texas hits us, Earth would still be a more pleasant environment than Mars could ever be.
Besides that, instead of financing a colonization of Mars, they could as well finance a mission to destroy the meteor or change its course.