Yes, think about it this way. If you were on a flight from say, New York, JFK Airport (KJFK) and you were flying to Miami International, (KMIA). Those crafty folks at your airline's dispatch would have already provided your pilot with a list of suitable diversionary airports for every phase of flight tailored specifically for the plane's type, weight, cargo, fuel burn, weather and several other fun factors that go into the cost of your ticket (and the revenue level of the plane, haha!). 

So putting our scenario over here in the States let's just say our origin flight (the one containing most of the characters accepted thus far) took off from New York and happily headed south along a pre-planned route through the air and somewhere over South Carolina the pilot noticed something not quite right or there was an unruly passenger- whatever the case, one of the diversionary airports would be used at that point. In this scenario, let's just say that was Savannah/Hilton Head Intl (KSAV). 

In the States there would probably be another plane dispatched or the passengers would be moved to a plane in Jacksonville, FL to finish the trip to Miami. You'd be surprised how many different contingencies there really are for EVERY situation. It's not quite as messed up as you think, but I'm getting off topic. 

For our story the diversion of the [i]originating [/i]flight and the [i]transfer[/i] of some of the passengers to a smaller plane to reach the "hub" destination  of Lhasa (ZULS) is where the terror begins. Because I am a dork, I know that nothing flying out of Beijing Intl (ZBAA) is probably going to be smaller than an Airbus A330 or a Boeing 777 which would cruise at around 35k. The most plausible destination (and this just a guess on my part) for this plane would be New Dehli Intl (VIDP) so we would have some characters that would be planning to go any number of places from there. There might be some options given, but we're just going to say that our characters chose to take the ferry flight for one reason or another. Maybe they're in a hurry, or got lucky or whatever. We're not going to fit the passenger load of a wide-body jet into a DC-3, but story-wise it sets up our scenario nicely. 

Since I'm back at home base now I can look at a couple route maps for Tibet Airlines and Air China and find us a real diversionary airport where our characters would have boarded the forlorn DC-3.

For fun you can plug those four letter airport codes into google and they will pop right up on the map, just try it ;-)