Other mistake: When Wendy and Kevin are grabbing lunch, just before Frankie Cheeks dies, the guy asks to take their orders (via the microphone) Wendy and Kevin never reply throughout the rest of the scene, and they are at the restaurant for at least another 2-3 minutes (during the whole of Frankie's death sequence) The guy working at the restaurant must be extremely patient not to ask for their orders again.
Other mistake: When the coaster is stuck upside down on the loop during the premonition, Wendy looks down at the track. The track shown is not what a loop would look like from above, as there is no entry/exit point; the track would not go straight across as shown.
Other mistake: During the premonition when the coaster is stuck on the loop, Wendy looks down to see a curved track piece with several bodies on the ground. She and Ryan then roll the coaster backwards, which results in Ryan's death and the coaster derailing. As Wendy falls, it shows the exact same piece of track and bodies despite the fact that the coaster travelled backwards a fair distance.
Chosen answer: They would've died, but Death "knew" they wouldn't have stayed in the car. If they had stayed, Death would change his death.