Imagine if they are all really in hell. In hell because they are forever trapped between the eternal conflict of the 2 Gods. And besides that they are trapped with other humans...worse.

So in the end they won't eradicate the white walkers. They'll just "lose" and sleep for a couple more hundred years until the other long night comes.

On the other side, if the white walkers win this will all be over, the shadow will engulf the world with Ghost Grass growing everywhere!
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White Walkers can eat ghost grass to turn human and it all repeats from the beginning.
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