The doomsday theorists may very well come up with a new theory so they can keep the end of the world stuff going in future years.
As for me, well, I don’t expect anything on terms of the world ending, more like just another day on the calender, though from what I’ve read here on the internet and in bathroom readers the theories range from unenlightened people being taken away on silver ships to people supposedly turning back into furry creatures or even Dragons. (the latter also being tied to reincarnation belief and possibly to the theory of a new spiritual age that some ancient texts claim will start on the 21st).
I also noticed meanwhile that the discovery channel and history channel here in the US are doing an entire week of doomsday shows that will end late afternoon on the 21st (which they will resume more normal programming if the world’s still here), there’s also been reports of archeologists reportedly planning to take a crystal skull to one of the Mayan temples (which could possibly lead to conspiracy theorists crediting its return for saving the world if it’s still here).
I do consider myself skeptical of all of the things written above though.