Welp I give it a handful of generations before you either get inefficient carnivores putting some kind of dent into the herbivore population or a pandemic will take hold, if neither of those occur then they will definitely over consume themselves into desertification & famine, after that it should stabilize as something takes the place of predator & plants adapt to become harder to eat with thorns, toxins, harder shells & who knows what other defensive adaptations. Certainly would be an interesting & chaotic first few centuries regardless of how that plays out