Human civilization
will terminate in a number of possible ways...
+ The Malthusian catastrophe (human population exceeds agriculture production) (the most likely, and most inevitable).
+ A "super plague".
+ A massive meteor impact.
+ Widespread large scale nuclear warfare.
+ Or, ultimately, the Sun goes nova.
The list is almost endless, these are just the ones that came to mind.
But, the end of the Aztec calendar does not foretell our doom.
I do have a keg party planned with my friends on 12.21.12 (it's a Friday night), but I don't have any plans to borrow a million dollars from a loan shark in the weeks leading up to the event.