My old team kept a centrally located out of office calendar so you would know who is out when. On 12/21, he wrote "end of the world, no work" and drew and arrow through the rest of Dec.
The only thing I'm wary about on 12/21 are the CRAZIES. We were out in the city last years on NYE and we saw lots of crazies with end of the world related signs. They make me more uncomfortable than anything. I'm seriously considering driving to work that day to avoid public transportation.