Coelacanths and crocodiles.
Not wholly sure what point you're making, but mine is relatively clear - the "Mayan Long Count" calendar wasn't terminated by the conquistadors and nor will it come to an end when the 12th B'ak'tun finishes. No calendar will end until time does, since a calendar is merely a subjective way of marking the passage of time objectively. So long as we're able to determine the arbitrary start point used and the manner in which the units are logged, we can calculate any date in time on any calendar. We don't use the Julian Calendar any more, but today is 20th September 2011 under it. It's 7/9/28/78 on the Chinese calendar and 5/7/5772 on the Hebrew one...
Our calendar will run out of suitable existing digits long before the Mayan Long Count. All we'll do on 31/12/9999 is add another digit to it - which won't prove necessary for the Long Count for another several thousand quadrillion years.
Assuming that Earth calendars have any real meaning by then, natch.