If you bother to take the story of Nightmare City to its "logical" conclusion, the vampires in this movie will eventually reach a problem of diminishing returns.
As the vampires claim new victims for blood, most of the those victims will come back as vampires themselves. Not every one will as we saw that one policeman who was beheaded before drinking his blood. But, most will, since the vampires, most likely, have no idea that they create more of themselves simply to injurying their victims. Eventually, what will happen is that everyone will be dead or converted into a vampire.
Without new humans to create more blood in their bodies, the vampires will run out of a vital, necessary for life sustaining supply. Then, the vampires will eventually die because as was stated in the movie, radioactivity destroys red blood cells in very short order.
Every indication in the movie is that though these vampires can fly planes, drive cars, and use guns, they don't have a high level of intelligence. They can't even speak. So, they most likely have no idea that those they kill will become competitors in the environment for uncontaminated blood.