Fire and blood ÔÇö three dragons wake
Daenerys walks into her husband's pyre with three fossil eggs and comes out at dawn unburnt, with three living dragons on her. Magic, which the maesters had comfortably declared dead, returns to the world on the same night the last dragonlord's daughter has nothing left to lose.
The fuller tale
Drogo took a wound in a fight he did not need to have, and let a slave woman he had spared treat it, and she did not treat it. When it went bad, Daenerys traded a life for a life in a rite the woman told her would work, and it did, in the way such bargains always do: the khal came back breathing and empty, and the child in her womb came out wrong.
The khalasar broke up, as khalasars do when a khal cannot ride. What was left was a few hundred old men, women and slaves, three fossilised eggs that had been a wedding gift, and a woman with nothing to lose.
She built her husband's pyre, put the eggs in it, tied the woman who had done it to the wood, and walked into the fire. In the morning the ashes were cool and she was sitting in them alive and bare, with three living dragons on her ÔÇö the first in a hundred and fifty years.
Magic comes back
The Citadel had spent a century and a half quietly congratulating itself that magic had drained out of the world. The maesters were right that it had gone and wrong that it was gone for good, and it returns on the same night in a burning field in the Dothraki sea.
It comes back everywhere at once: glass candles that had been dark for a century begin to burn at the Citadel, the red priests' fires start showing things, the woods witches are suddenly right. And beyond the Wall, whatever had been waiting eight thousand years starts moving.
Elsewhere in the wiki
 See the world as it stood in 298 AC What became of it  if an ending is written, it is here. Spoilers.
The chronicle records no ending here ÔÇö or none the maesters have set down.