Warning: SPOILERS for Jurassic World: Fallen Kingdom are ahead!
As what was expected to happen once the Indominus rex got loose and the other dinosaurs escaped, Jurassic World ultimately saw the same-named theme park being abandoned, but it wasn't our last visit to Isla Nublar. Jurassic World: Fallen Kingdom took us back to the island when Claire Dearing Owen Grady and their team tried to rescue as many dinosaurs as possible before the volcano erupted, but even before all that, the sequel opened with a team of mercenaries going to Isla Nublar to retrieve DNA from the remains of the Indominus rex. However, unlike the main events of Fallen Kingdom, which (just like in the real world) are set three years after Jurassic World, producer and co-writer Colin Trevorrow says that the opening scene is set not that long after the preceding movie. Trevorrow explained:
The opening sequence is set just after [Jurassic World]. There's 3 years that pass. We didn't put that type up onto the screen, but the opening sequence could even be weeks after or a month after, and then time passes to allow them to create that creature.
Needless to say that the mercenary expedition at the beginning of Jurassic World: Fallen Kingdom did not go as planned, and along with several of the crew being killed by the underwater-dwelling Mosasaurus and the Tyrannosaurus rex, the gate that had previously blocked off entering Isla Nublar didn't close all the way, allowing the Mosasaurus to get out. But during his appearance on The Empire Film Podcast, Colin Trevorrow clarified that the opening scene takes place only a few weeks, or at most a month, after Jurassic World. As a result, Eli Mills and his scientist have spent the following years creating the Indominus rex's successor, the Indoraptor, hence how it was ready to be shown off to bidders in the latter half of Jurassic World: Fallen Kingdom.
As for what the Mosasaurus has been eating since it escaped, Colin Trevorrow mused that the creature could have snatched up some birds, nesting pteranodons and other animals near the shore. But with Isla Nublar's destruction, the Mosasaurus has now ventured into new waters, and at the end of Jurassic World: Fallen Kingdom, the creature ate some surfers at a nearby beach. Just like the other surviving dinosaurs who are now roaming free on the mainland, humanity will need to get used to the Mosasaurus swimming around and preying on folks like a prehistoric, juiced-up Jaws.