They all check their smart phones to call for help and find they have no coverage. They decide to explore, maybe finding a tower somewhere. Instead they stumble onto their worst nightmare...a group of boomers sitting around drinking beer, smoking weed and playing shuffleboard....I'll finish now as I don't wish to bore you.
The Millenials will reject the Boomers' solution and come up with their own.
At the end of the movie, it will show bodies lying on the beach, waiting to be washed out to sea. On another part of the island, we see there was a bridge to the mainland. The final scene has the camera panning in on the only person left, driving over the bridge back to civilization.
LyricalOne 