The Wall comes down
Eight thousand years of ice ends in an afternoon, brought down by a dead dragon with blue fire. Whatever the lords in the south are arguing about becomes, abruptly, a secondary matter ÔÇö though it takes most of them a while to notice.
The fuller tale
A small company went beyond the Wall to capture a dead man, on the theory that the only way to make the south believe was to show them one. It half worked: they got their proof and they lost a dragon doing it, and the dead thing they carried back convinced almost nobody who mattered.
Viserion went down through the ice of a frozen lake with a spear in him, and the enemy pulled him out with chains, and what came up was not a dragon any more.
He brought the Wall down at Eastwatch in an afternoon. Eight thousand years of ice, whatever had been woven into it, and the whole purpose of the order that had held it, ended in a few passes of blue fire with the army of the dead waiting on the ground below to walk through the gap.
What it meant
Every argument in the south ÔÇö the throne, the succession, the alliances, the debts to the Iron Bank ÔÇö became a secondary matter at that moment, and it took most of the people having those arguments a considerable while to notice.
It also ended the Night's Watch as anything but a name. The order had one function; the thing it guarded no longer existed; the enemy it was founded against was on the wrong side of it.
Elsewhere in the wiki
 See the world as it stood in 303 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.