Why do you think your dog ate your rooster?
If the bird is gone, I would think it more likely something like a fox or coyote or some other predator got your rooster. Dogs tend to just kill the animal and not eat it.
Even if it was your dog, it is too late. Too much time has passed and there is no connection to chasing an killing a chicken and whatever you intended to do to the dog.
Your dog might have disappeared for a couple of hours because he was investigating the predator that was in your yard.
Ok I have to disagree (no offense) if the dog is acting sheepish then he did something wrong and he remembers it regardless on how much time has passed!
If the dog acts like he did something wrong you can usually tell by their demeanor... i.e. putting his head down when approached walking sideways licking his chops while holding his tail between his legs