Anything is possible, but my guess is that if they were hijacked, they had a plan that went wrong. It's far more likely, and it's happened before: http://en.wikipedia.org/wiki/Ethiopian_Airlines_Flight_961
- A depressurization event, either as a result of an accident or a botched hijacking (see https://en.wikipedia.org/wiki/Helios_Airways_Flight_522)
- Pilot suicide, with a somewhat unexpected signature (see https://en.wikipedia.org/wiki/EgyptAir_Flight_990)
Pretty much anything is possible, indeed. However, I'd recommend this post on airliners.net for a comprehensive sanity check: http://www.airliners.net/aviation-forums/general_aviation/re...
But: Wikipedia on water landing (ditching) shows a high survival rate http://en.wikipedia.org/wiki/Ditching#Passenger_airplane_wat...
I'm confused.