Revealing mistake: When the plane first lands at Bangor airport, the words 'American Pride' on the plane are reversed, like they are reflected in a mirror in one shot as its wheels hits the runway. (00:50:55)
Other mistake: In the scene where they are 1st landing at Bangor it is known that there is no electricity at the airport. If you look closely during the landing you will see that the runway lights are on. (00:50:40)
Factual error: When initially investigating the missing people and the condition of the airplane, Brian looks at a screen that gives the airplane's transponder code (or "squawk") as 7777. An airliner would never be squawking that code, since this particular code is reserved for military interceptor operations.
Answer: No, they didn't die. The premise of the story is that the sleeping plane passengers were in an alternate timeline a few minutes out-of-sync with normal time; so, when they awoke, they were aware of a dead zone in the immediate past. Everyone else in the world is still alive in the present. The "Langoliers" were interdimensional creatures that fed on the past, gobbling it up like a stage-cleaning crew.
Charles Austin Miller