it comes down to Verin's Tel'aran'rhiod paradox. The Dark One is free in all worlds, or he is free in none. If the Shadow kills or Turns Rand he cannot choose to give Shai'tan victory. So he'll destroy this world, but in countless other variations, he does not and so he remains imprisoned. The thing with the worlds of if is not that this world is more real than the others, it's that the Dragon never chooses to allow Shai'tan victory. In all those worlds where Ba'alzamon claimed victory, the Shadow destroyed the world or killed Rand or anything, but Rand never gave in. In all those possible worlds Shai'tan created in their final confrontation, Rand refused them all.
~Master Splinter
Victorious in Bergioyn's legendary 'Reverse Mafia'. *MySmiley*