One interesting theory I saw somewhere that could shift the axis is the whole notion of a pact of an uneasy peace between the First Men, the Children of the Forest and The Others, to essentially mind each other's own business. The Wall is there to keep the men from conquering the far north since that is where non humans dwell and in the past, men have been known to slaughter and not be very interested in working together. It is not there just to protect from the Others coming down but also from humans going too far up. The Wildlings survive up there because they make sacrifices to the Others, paying them respect and fear.

Dany and her dragons are capable of wrecking that pact, which would in turn unleash the full fury of The Others on the world, so instead of saving the world, she'd unintentionally bring about its ruin. Stopping her is the only thing that will keep the world from falling in to total disaster... making her a sort of de facto villain.

If this holds true, what I could see happening is that Jon Snow is brought back as a figurehead for The Others to combat Dany with only someone in a neutral position (Bran? Tyrion?) being able to keep them from destroying each other and in turn everyone.

The series is called a Song of Ice And Fire, which to me could mean that, like any song, there is a mix of chaotic different notes and instruments (humans, dragons, Red God, Drowning God, Others) that somehow finds a perfect balance and turns into something greater than any of its parts.