Ah, Schrodinger's cat. Put a cat in a box with poison released randomly (reasons of quantum uncertainty)... and then close the box so it's unobserved. Since the time at which the cat dies is unknown (random, and unobserved), it can be said that the cat is in a state of both death, and not death until observed.
It's also the reason Niels Bohr walks among us, immortal and unobserved... much to http://dresdencodak.com/cartoons/dc_022.htmSokar's lament.
...
Okay, so it's an acquired sense of humor.
Anyways.. I think the point he is making is that the "off-screen" PCs (those of the ones that aren't there), are off doing their own things and thus absent during the in between times that they aren't there.
So the session would end in a normal situation (not about to open a door in the middle of the dungeon, rather, at the bar of a tavern, etc). Then the next session, that player is absent, so then his Character is as well... and that's when you roll to see what happened to him.
If I ever start a Dungeons and Discourse game, you can bet I'd use something like that... if only for the Schrodinger Cat reference.
Although, an ingenious player might refuse to come back until something new was rolled, stating that until he came back, he's unobserved, and therefore immortal. /slap
