Here's some REAL Wild Mad Guessing for ya:
In Episode 3, Gordon, Alyx, and Barney all make their way to the Arctic, and bump into Chell, who teleported there using crazy Aperture Science technology (remember the Borealis is from Aperture Science.) They all proceed to have loads of wacky adventures.
Then, SHIT HAPPENS. The Combine win, everyone dies, and the Earth is exploded, Death Star style. Gordon (the last survivor due to his impenetrable HEV suit) then utilizes Cave Johnson's "trace amounts of time travel" to travel back in time to before Episode 3 was released and stop Valve from making the game, and tell them to CHANGE THE ENTIRE PLOT, thus preventing all those horrible atrocities from occurring.
... What do y'all think?
edited 3rd Dec '11 9:43:12 AM by ParkourPaisho