Dinosaurs are extinct. Extinction is forever. They cannot reclaim the planet.. There are nutty scientists who claim that birds are living dinosaurs, but these nutty scientists are cladists. Cladists have been severely criticized by Darwinians over the years as being insane, being religious, and being unscientific. Indeed, it is nothing short of insanity to say that birds are living dinosaurs, because even if birds evolved from a dinosaur (and there is a mountain of evidence that opposes that hypothesis), it does not mean that birds are dinosaurs.
After all, mammals evolved from a cynodont therapsid reptile, but that does not mean that mammals are reptiles. Similarly, dinosaurs themselves evolved from primitive archosaurian reptiles, which in turn evolved from a primitive diapsid. If we go back in time, all land vertebrates, including reptiles, amphibians, birds and mammals, evolved from a fish. So, why not say that human beings, birds, dinosaurs, lizard, turtles, snakes, frogs, salamanders and whales are all fish, if we insist that birds must be called reptiles?
Lastly, Dollo's principle states that evolution is not reversible. That means birds cannot evolve back into the same animals as their ancestors, no matter what that ancestor was. That is one more reason why it is insane to claim that birds are living dinosaurs. Birds evolving back into their reptilian ancestor is about as implausible as humans evolving back into a shrew.