It'd be funny if they decided not to kill him off. Keep his spot open for a possible return.

AMC Exec: "How about this, guys! Rick leaves the group to start his own business selling furniture made out of the rotting flesh of walkers! He returns three years later when he has to file for bankruptcy."

Either that or they could go full Bobby Ewing. Have Rick start season 10 in the shower at Alexandria having dreamt the last five years.