Warning: The following contains dino-sized spoilers for Jurassic World: Fallen Kingdom!
At the end of Jurassic World: Fallen Kingdom, Maisie makes a crucial decision that Claire couldn't and, in an act of compassion, releases the dinosaurs from the mansion. The weight given to this act seems to indicate that it represents a massive shift in the natural order of the ecosystem established through millennia of evolution. I believe Owen states that 'there's no going back.' Yet it was just a couple dozen dinosaurs set free; has the Earth truly entered a new era and become a Jurassic World as Ian Malcolm warns, or is he just overreacting?
Heading in to Jurassic World: Fallen Kingdom, the characters were grappling with an important moral question: whether to save the dinosaurs that we created or allow nature to remedy that which human hubris hath wrought, allowing the creatures once again to go extinct. At the end of Fallen Kingdom, this moral dilemma is rendered irrelevant for the time being as the rescued dinosaurs are now out in the world, roaming wild and free for the first time. Once again, Ian Malcolm has proven prescient and the events of the film represent a crossing of the Rubicon. The toothpaste is out of the tube now and there is no going back with the dinosaurs after Jurassic World: Fallen Kingdom. Extinction is no longer a threat and the dinosaurs will no longer be contained to one small island. They are here to stay. Here's why.
The Dinosaurs Will Be Difficult To Track Down
We don't know exactly how many dinosaurs were "rescued" from Isla Nublar, but it seems like they couldn't number more than 100 at most. So, in theory, that amount should be easy to find in the wild and recapture. After all, it's not like a T-Rex will go unnoticed at a zoo or Blue will blend into suburbia. However, there are several factors that will make tracking and capturing these creatures difficult. We know that the trackers in the dinos work in perpetuity, but the system seemed like it could only be accessed from Isla Nublar, which is under a fresh coating of lava at present. Also there is no organization actively pursuing the dinosaurs and they could spread far and wide before the DPG or the government mobilizes. The survivors of the Lockwood estate incident probably don't know the exact count of the dinosaurs in the wild. Plus, if this series has proven anything, it's that dinosaurs are difficult to track, capture and kill.
The Island(s) Is Still There
We all saw Mount Sibo on Isla Nublar explode in Fallen Kingdom, killing countless dinosaurs in an absolutely heartbreaking scene. However, I struggle to believe that the volcano completely wiped out every dinosaur on the island. We saw dinosaurs fleeing into the sea, so is it not possible that any of them made it back to shore after the lava had subsided? Also was there no corner of the island that was untouched by the blast? There is also the fact that the Pterosaurs could have flown away to safety, to Costa Rica or perhaps Isla Sorna. The site B island has basically been ignored in the Jurassic World series but the DPG website indicates there was a drop in population on Isla Sorna and the remaining animals were transported to Isla Nublar. But even if that is true, the Pterosaurs could at least fly to that island temporarily during the explosion. The very assumption that both island's dinosaurs are completely extinct leaves room for a nasty surprise when some find a way to survive.
The second half of Fallen Kingdom revealed the true plan of Rafe Spall's despicable Eli Mills: to sell off the dinosaurs rescued from Isla Nublar to the highest bidder. Buyers from around the world, all with mustache-twirling villainy, arrived at the Lockwood mansion to offer millions for the prehistoric creatures so that they could use them for unknown purposes. A lot of these dastardly dignitaries met a deserving end when the Indoraptor and other dinosaurs were set loose, but as we saw, many of the dinosaurs they purchased had already been packed into containers and shipped out. The efficiency of the operation means that an unspecified number of dinosaurs are now spread throughout the world, likely on multiple continents, perhaps untraceable. And given the nature of the buyers, they probably won't be too keen to give the dinosaurs back. We also don't know if these buyers will try to breed any of the dinosaurs or reverse engineer the de-extinction process, leading to more dinosaurs in the world.
InGen Is Still Out There
Most of the villains in Jurassic World: Fallen Kingdom died onscreen in brutal fashion, but Dr. Henry Wu, the franchise's resident mad scientist, is seemingly still alive. Like life, Henry Wu always finds a way. We don't know the official status of InGen and whether or not it is still a part of the Masrani Corporation (or if Wu and team were working independently), but the point is that as long as there are geneticists, and specifically Wu, with the know-how to de-extinct dinosaurs and create hybrids, there will be a market for their talents and dinosaurs will endure. It's likely that Henry Wu escaped with the DNA samples from the lab in the Lockwood mansion and maybe even some of the eggs that contained who knows what. However stupid, the notion of hybrids and weaponized dinosaurs has been put forth and there is no going back. It is like nuclear power, once it is discovered there is no closing Pandora's box.
Life Finds A Way
Ian Malcolm's theory that life finds a way has proven true throughout the course of this franchise. Life finds a way to escape, to survive, to breed. In the first Jurassic Park, the female dinosaurs changed sex in a single-sex environment in order to breed. I expect that whatever genetic checks against uncontrolled breeding have been put in place since then are far from absolute and the dinosaurs will find a way to procreate and advance their gene pool once again. And since dinosaurs haven't existed alongside modern mammals and reptiles, we have no idea what kind of interspecies breeding is possible. Dinosaurs are re-inheriting the Earth and they are essentially an invasive species, and like all invasive species, once they gain a foothold, it will be very difficult to get rid of them. As long as there is a single dinosaur left in the world there is a chance that the species will somehow continue, creating the titular Jurassic World.