I'm setting up a doomsday bunker that's completely sealed off from the rest of the fort. Four dwarves will live inside, and if anything Fun happens to the fort, they can stay alive until migrants come to take back Tangledarrows.
An update: a vile force of darkness arrived in Tangledarrows. My military sucked so I closed the drawbridge, trapping a few unlucky dwarves outside, who were then cut into pieces by the goblin forces. All the barrels were sitting just outside the gate, so it wasn't long before we ran out of booze. Citizens were rioting in the streets, so it was clear something had to be done.
The plan was simple: unleash an unholy army of demons from the depths of the earth to battle the goblins. Our two enemies would destroy each other (and likely most of the fort), but 4 dwarves were still sealed away in the Doomsday bunker, so Tangledarrows would live. We sent a miner deep into the bowels of the earth, through a passage filled with unbearable heat and and the shrieks of dark, undwarven things. We never heard from him again. Soon, demonic creatures came up from the tunnel and began slaughtering dwarves left and right. We opened the drawbridge and goblins began pouring in from the other side. Soon, in the main dining hall, the two evil forces converged and killed the rest of the dwarves. The halls were thick with smoke and the stench of rotting corpses. They then turned on each other, the demons killing the goblins before they could escape.
Some time later, even more goblins arrived. With them was the leader of their civilization: Ciwa the Badger Fiend. For reasons unknown, his army turned on him and after a lengthy battle, he was struck down. They then stormed into the fort to battle the demonic horde. Most of them were burned alive, but several managed to escape.
Meanwhile, sealed away in their bunker, the four remaining dwarves are beginning to get restless and unhappy. They are tired of living in cramped conditions, eating only withered plump helmets. They swear they can hear the ghosts of their dead friends.
And some migrants have arrived.