Debbie the dog is referenced throughout the film, although we never truly see her. At one point when Dan is jogging he sees something in the grass. The camera briefly cuts to it (52:53) but it is very hard to tell what we’re looking at and it in no way looks like a dog. However, it is later implied that it was the remains of the Debbie the dog. So yes, the dog dies, but we never meet the dog and it’s death is not shown on camera.