The Long Night comes again
The living make their stand at Winterfell in the dark, and lose most of it, until a girl nobody counted ÔÇö trained by assassins she left behind ÔÇö puts a Valyrian dagger where it needed to go. The war that the whole story has whispered about since its first page is decided in a single night, in a godswood, by the smallest person present.
The fuller tale
Everyone who was left came to Winterfell: northmen, free folk, Unsullied, Dothraki, knights of the Vale, two dragons and a great many people who had been trying to kill each other the previous summer. They put the crypts behind the walls, which turned out to be a poor idea in a battle against an enemy that raises the dead, and they waited in the dark.
It went badly from the first minute. The Dothraki charge went out into the black and was simply extinguished. The trenches were fired too late. The dead came over the walls in a mass that made the walls irrelevant, and the fighting went from a battle to a retreat to a last stand in the space of a night, and the dragons could not tell friend from enemy in the storm.
It ended in the godswood, where the enemy's commander had come for the boy under the weirwood, with every guard around him and the whole night gone quiet. A girl nobody in that yard had been counting ÔÇö a Stark daughter who had spent four years being trained as an assassin by people she had walked away from ÔÇö came out of the dark with a Valyrian dagger and put it where it needed to go, and every dead thing standing in the North fell down at once.
The war that was always coming
This is the war the story has been whispering about since a ranging in its first pages: eight thousand years of prophecy, an order sworn to it, a wall built for it, and it is decided in one night by the smallest person present with a knife that had been passed from hand to hand since it was used on a crippled boy.
It is worth saying plainly that the cost was enormous and that the realm's response was to go back to arguing about the throne within a fortnight. The dead were burned in front of Winterfell, the survivors got drunk, and the next war started before the pyres were cold.
Elsewhere in the wiki
 See the world as it stood in 305 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.