The demo was a full version of the game until they released the 'special edition', which finalizes and adds new features. Assuming they haven't changed the demo directly, you can easily get to the end of the game through the demo and enjoy all of the endings (though the special edition may have added more, waiting for all of the 1.x patches before buying). If you are stuck, I suggest following http://outbreakgames.wikia.com/wiki/Snow_Daze:_The_Music_of_Winter_Walkthrough, it got me to the end of it.
*oh that crash, forgot about that, assumed my download failed. I just clicked ignore and forgot about it though.