If the DM is gone, we cancel gaming.
If the host is gone, we cancel gaming.
If 2 or more players (we have 5) miss, we cancel gaming.
If 1 player misses, we continue, and he is an NPC under the control of another player they designate. The entire group chimes about the manner in which the PC is RP'd.
I am the current DM, and we've only cancelled 5 times since the campaign started in July, and this week was our 30th session!
Sakkara