So, I just left the back door to my fortress open and a 50-ish strong goblin siege showed up with like 12 trolls. I didn't even think sieges could BE that big.
It went very very poorly.
I forsee a tantrum spiral, literally everyone is <30 happiness and most are at 0. Continue and you will understand why.
I started with 283 dwarves.
I won, but with 33 dwarves left. 30 military, 3 civilians.
I can't even BEGIN to bury all these dead. I just can't - there isn't the dwarfpower left to do it. I have one legendary mason left and almost all of the rest of the survivors (except for two recent migrants) are military. And THEY even got hit hard. The halls are literally covered in blood.
To expand:
The siege showed up. I deployed all my forces, and sat back to watch a good show. Then I got a message that my strand extractor had died.
The back door was open, but I got an understrength melee squad (mainly made of recruits) there right away... and they got horribly slaughtered, despite being skilled and in Candy armor, because they were outnumbered handily and got surrounded (it was rather like watching an amoeba eat something).
The rest of my squads were still en-route from the west keep. The goblins and trolls reached the main stairwell. Job cancellation spam ahoy!
Three trolls went up, five trolls went down. I didn't even try to count the goblins. They also had a dwarf that had been previously snatched with them. The dwarf went down.
Down into the living areas. This was the most concentrated slaughter - trolls breaking down people's doors and killing them in their beds, ext. In my pursuit of an efficient design, they had no other way out. One third of the fort died right there.
Then they reached the trade depot. and killed the merchants who had just unloaded. One of the merchant guards killed a troll here, before having his head relocated off his body by a goblin axeman.
Up above, the trolls killed a few dwarves who were hauling in my stockpiles on the floors above there. In the main entrance to the east keep, they smashed floor grates in just the right places to block my squads who were almost across the bridge at that point (but not quite). My marksdwarves got a troll and a handful of goblins here.
Below in the living quarters, the slaughter continued.
I directed one of my miners (also skilled to 3 in masonry) to dig out into the lower caverns and wall himself in the passage he dug. He completed the wall on the mine side just before a goblin rounded the corner, but a GCS ate him from the other direction before he could finish the second wall.
My squads are now having to take the long way through the tunnels. Compare 250 steps using the bridges to almost 1,000 - and they were half way across the bridge, so even more than that.
Another troll, clearly too dumb to find the back door, began beating on the front gate. It's legendary quality Candy, he's gonna be there a while. Why didn't my traps get him?
Even while the slaughter was still continuing in the living halls (the death halls?), a troll wandered down into the dungeons and began killing the 14 prisoners, the 2 guards were helpless (they had inferior equipment).
Many other dwarves were dieing in other hallways of the fortress at this time.
Three trolls found my magma forge area and began smashing the metalworking equipment as a few goblins found the unlocked door to the metal stockpile where my metalworkers were hiding...
I watched as an axegoblin cut a Dwarven child in half. A troll punched a cat over 40 tiles.
Somehow a fire started and began to spread in the wood stockpile level. Now everything is obscured with smoke. A dwarf falls down a well.
The trolls and goblins reach the noble's living quarters, and nothing of value is lost.
My squads have reached the lower mines, and begin to clean up the goblins and trolls there. At this point, I'm down to 79 dwarves.
I manage to wall a mason and one other civilian in the end of a hallway.
A troll somehow found its way deep into my mine works, and smashed the floor grate sealing the stick of a Candy vein, letting ~150 clowns into the fun.
My military is tied up with the Clowns now.
50 dwarves. Almost everyone is dead. The floors are covered in blood, and there are four bodies at the bottom of the well. Somehow, magma is flooding the forge area. Water is gushing in 3 or 4 places due to smashed doors and floodgates, and my frame rate is going to hell.
The water dams the magma, preventing it from blocking the main stairwell.
The clowns are dealt with, I take one civilian who had fled into the mines and have him replace the floor grate with a true floor.
My military heads up the stairs, clearing out goblins and trolls relatively easily, and 20 minutes later the fortress is secure. I position a melee squad and a squad of marksdwarves outside the back door (the trolls broke the controls for it, I can't close it).
There is still a troll in the dungeons, but I have not killed him yet as there is nothing left for him to destroy.
And, finally, I have time to breath and I realize how bad the last hour was for this 14-year-old fortress.