Yep. calendars end. simple as that. why does there's last so long? better at predicting future events than we are, maybe. our calender lasts 365 days. what happens when it runs out? we get the next years calender.
What happens when the mayan calender ends? people panic. people make a lot of money. people laugh. and most aren't doing all 3. The preparation no one has dealt with is just getting a new calender. (I know, that would require finding real, surviving mayans, as they were way back when).
Now, if, in some freak random event, we HAPPEN to die in 2012, then hey, we won't be around to argue the next "end of the world" date.