Rocks fall, (almost) everyone dies
First, he took care of Ed. Her real name was in her memory, not the school directory. And then he wrote down every staff member, followed by the student body. The Death Note never ran out of pages, no matter how many people he wrote down.
Light had no idea how much time passed as he took care of affairs, deliberately leaving one name for last. But when he went to write Lelouch down, his hand seemed to have other ideas. It was only after his own name had been written down that he became aware of it.
Forty seconds later, he slumped over his desk, pen still in his hand.
[OOC: Feel free to comment saying where your characters were when they died or how they react to surviving. Wolfie, can Lelouch be the one to find Light?]