Well, just going by the previous films, there are already raptors loose somewhere around San Diego (the T-Rex couldn't have taken out the crew of the InGen ship in The Lost World
) --though that ball was totally dropped by Spielberg-- and pterosaurs flying toward Central America while a hundred armed Marines just smile at them from machine gun equipped helicopters at the end of JPIII
for some reason.
InGen would have to be broken as a corporation by this point after so many blunders, but there's still that rival company that was hinted at in the original Jurassic Park
(the guys Nedry was planning on delivering the dino embryos to). I could see them setting up a dino smuggling operation and bringing the dinosaurs back to their lab(s) on the mainland around the world, where some of them are able to escape, either on their own or more likely with the help of idiots like Vince Vaughn's character. That way you could introduce a more varied mix of escaped dinosaurs than just raptors and pterosaurs if you want, which could get boring.
I could see the military bringing in people like Grant, Sattler, Malcolm, Harding, etc. as experts on dinosaur behavior so they can hunt them down and capture or kill (last resort with the scientists around, probably) them with special forces teams. Sort of like a fast reaction force to reports of dinosaurs on the loose. The kids from the previous movies could even get in on the action now that they're all adults (Joe Mazzello has a pretty prolific acting career going now).