In most of our campaigns, absent player's PCs usually fade into the background -- they travel with the others but aren't specifically mentioned (if possible), don't act, and aren't harmed but also miss out on decision-making, loot (unless others share later) , and the fun of the game. Occasionally, they may run a side quest of their own to explain their absence or get left someone they can return from. In one campaign, we had device the players nicknamed the Poke-ball that absent players went into and another carried with them.