On a long enough timeline, the survival rate for every fortress drops to zero.
The relentless wearing down of the fortress has reached its breaking point. 37 ghosts of various dispositions haunt the dome, and one in particular has already claimed many dwarves in its hatred for the living (that's about 1 ghost to every 4 dwarves - the current fortress population is 144). The dead cannot be stopped, and so the destruction of Weatherwires, no matter how much the dwarves try to build it back up, is ultimately inevitable. It was decided decades ago that on this day the barriers holding back oblivion would be released, and Weatherwires would find its end not in an agonizing whittling down over the course of decades, but in a fiery blaze of glory, a clash of demonflesh and adamantine which would echo in the dome for eternity.
The military assumes positions under the command of Libash Dippedurns the Ageless Deep of Rhymes. Every squad at the commander's disposal is positioned along the length of the narrow passage into which the enemy will pour. Libash knows that if but a single demons were to break past his defenses and into the vast hollowness of the dome, her forces will be useless - the fiends would simply fly throughout the grotto and pick off dwarves where they stood.
Immediately to the north of the breach is positioned the Silvery Princesses. To the south, Libash and her surviving squadmate, Shorast Sealmet are positioned alongside the Silvery Skunks. All of these dwarves - even the new recruits - possess legendary skill in their respective weapons.
Behind Libash and her compatriots are positioned the Lone Lashes, now comprised almost entirely by the only survivors of clan Lashhushed. They, too, are legendary warriors, despite having only trained for a few years. The captains are apparently stellar teachers.
Positioned behind the Silvery Princesses are the prince and his squad, the Royal Fortresses. Many of these recruits are now legendary axedwarves, but poor Logem "Quakedented" Sparkswords has only been in the squad for a few short months, and possesses no military skills whatsoever. Kol "Languagemetal" Claspedrelief, however, has only grumbled and shirked his training, so despite being in the squad for longer than any of the Quakedented children, he is only a competant axedwarf. Presumably his coddled childhood as the youngest dwarf resulted in a spoiled brat with an over-developed sense of entitlement - in which case, the coming battle will be a sickening wake-up call.
Asmel "Murdershot" Deathchannels, prince of Weatherwires and son of the old duke, thinks back to the days of his youth. He remembers running along the rim of the caldera in the diffused light of the upper fortress, laughing with his brother and sisters, and the other friends of the Murdershot children - Kogan "Ceilingintense" Toolfriends, whose parents died in a cave-in, leaving him orphaned; and Lòr "Lensnarrow" Gearslings, with whom his sister Cog, now the queen, had had a brief affair. But now his siblings were dead, Cog was most likely mad with power, and their friends had gone mad and withered away from thirst or starvation in the tantrum spiral during his childhood. Soon, he would meet them again in whatever afterlife Baros Buriedplagues, the god of death, saw fit to grant him.
Commander Libash has no illusions about this conflict. She knows that the chances of the dwarves winning are slim to none - but she does not confide this in her squadmates. She only rails them onto victory, claiming that this shall be their hour of glory, even though she knows deep in her soul that she leads the last of her civilization into oblivion. Vabôk knew that the fight was unwinnable too, she suspected, although he would have never said it. They were squadmates, not friends - dwarves like Vabôk and Libash, who spent years doing weapons drills over and over, had no friends.
With a heart that felt like it was made of slade, the commander issued the signal to deconstruct the wall. Shorast Rockclearings, a merchant guard turned stonecrafter, moved forth and began to tear down the rough obsidian block wall.