In one of my games, a spellcaster died and was later resurrected. Upon resurrection, her familiar (a cat) returned to her several weeks later. Behind the scenes, I ruled that her familiar simply became a normal cat, and upon her resurrection, "reawakened", regaining its identity, memories, etc.
For flavor, I also roll randomly (10% chance) to see whether or not a called familiar has had a previous master. If so, the familiar may be able to recall small memories of its former master and its former life. It adds at least a small amount of flavor, and that's rarely a bad thing.