I was watching through a recap playlist of Disney villains (and still am as I write this), and the title of Happy Dan came up with the channel saying they were not able to find the book. While I have only done a brief look into, I cannot say if it is truly lost and figured I should take it to these forums for confirmation before going on a search that may be pointless if it is found. As I know, the book surrounds either being the inspiration to the movie The Lady and the Tramp or was inspired by the movie. I do know that it focuses on the film.
Should post this brief update here on it. The Happy Dan book can be seen as part of the inspiration towards Lady and the Tramp, which is written by Ward Green. He has written a Lady and the Tramp book as well, but as I understand it is at Walt Disney's request so the audience will be familiar with the story by the time of the film's release.