They would have died or passed out right away from lack of oxygen.
I am afraid I do not think that is true (death) and even if they passed out at first, I do not think they necessarily stayed that way.
A teenage boy survived a flight from the US to Hawaii hiding in the 'plane's landing gear. The 'plane was flying at 38,000 feet.
http://edition.cnn.com/2014/04/21/us/hawaii-plane-stowaway/index.html
As unlikely as it sounds, officials believe the boy rode in a tiny, cramped compartment for almost five hours, at altitudes that reached 38,000 feet, without oxygen and in subzero temperatures
So this was someone remaining in sub-zero temperatures and depleted oxygen for hours and surviving. I accept that he must have been unconscious - that was because he would have remained at high altitude for the bulk of the flight.
Sadly, passengers falling out of a 'plane may be extremely cold and oxygen depleted at the start, but they are falling towards the earth at around 120mph, so the air is getting warmer and the oxygen more abundant as they fall. Nothing about the actual falling is life-threatening or likely to make a person unconscious, so as I understand things, sadly they may well actually regain consciousness even if they lost it when first coming out of the 'plane. The thing that kills passengers is blunt force trauma from hitting the earth or the water in most cases, or possibly from trauma caused by coming into contact with bits of the 'plane.
This is from a forum and is a quote about victims of the Lockerbie air crash:
I asked a cousin, an Air Force officer, what the victims of the Lockerbie/Pan Am bombing would have experienced. It's not fun:
The bomb used to take down the jet was fairly small -- just large enough to cripple the plane but not large enough to kill many people. He estimated that anywhere from 10%-25% of the passengers would have been killed by the blast or the break-up of the jet. A majority of passengers would have survived the explosion. Due to hypoxia they would probably begin to lose consciousness quite quickly, but only for about a minute. By then, they'd be at a lower altitude where they would regain consciousness. They would still have another 3 or 4 minutes of free fall where they'd be perfectly aware of what was happening to them. Many of them were still belted into their seats when found on the ground.
I realise that is not what everyone wants to think, but I genuinely do not think there are any credible scientific reasons why the passengers should just lose consciousness and remain unconscious and pain free in this situation, however comforting that might be.
Edit - just saw the link to an article in the DM claiming the missile would have damaged the plane so comprehensively that the passengers would have died instantly. This is a comforting thought, but he states that the missile strike would have 'shredded' the plane - I don't see how any of the bodies could have remained intact in that case, and at least some of them have. Also, from another post in here, (tragically) a foreign correspondent describes seeing a passenger strapped into their seat with a face 'frozen in fear' so I fear at least some of the passengers may have been conscious for much longer than we would hope.
I think an added trauma for the families must be the total shambles at the crash site. I would be beside myself knowing that my loved ones were just lying about with no proper professional salvage exercise ongoing. If this crash was anywhere else in Europe, retrieval of bodies and transfer to a proper morgue would have started as soon as possible - certainly within 24 hours. Not wanting to be even more gruesome than I have been - but people want to say goodbye to their loved ones - leaving them unrefrigerated will make this more and more difficult. I think all those poor people are still lying where they fell. Then there are random locals wandering around rifling through their things - those pictures of people standing on the fuselage and generally having a good old nose just seemed so disrespectful.