Although author Philip K. Dick (Bob) had an early-'50s short story titled "The Skull", there has never been a full book with that title published under his name.
This T.V. special works amazingly with as an episode of Moral Orel NOT as a stand alone short film just as El Camino: A Breaking Bad movie is not enjoyable if you have not seen Breaking bad. The characters are better than I remember and the animation is superb and the ending really hits home knowing the the context of Orel's future Arch.