I'm thinking about this because of my friends dog that got hit by the car and returned home after several hours. I've talked to her since then and she said she thought that after he got hit, he probably wandered off to die somewhere, and then fell asleep for a while before waking up and limping home. Apparently he has a lot more bruises/scrapes than they originally thought and he has some tissue necrosis (death) which they are trying to take care of before resorting to surgery. I'm really hoping he pulls through this!
Anyway, I have heard that cats will leave home and die away from their homes... wondering if dogs are known to do the same thing? What is the purpose of this behavior anyway?