Godlycooked saw its second siege just after a caravan arrived. It was far too large and well-equipped for my tiny militia to deal with, so I was forced to pull back and seal the gate. None of the merchants got in, although I think a few may have escaped the map. Those who didn't were slain outright or went melancholy. A caravan guard survived for more than a month, but eventually one of the enemy got a lucky shot on her and she fell. I've erected two slabs in her honor, one in the dining hall for everyone to see and another in the security office to inspire my troops. I later managed to recover her remains and seal them behind glass, but the relic seems to have rotted away to nothing.
While the siege was parked outside, I spent my time on internal infrastructure, especially plumbing, which involves the most complicated waterworks I've build since my very first fortress in 40d. I've been spoiled by aquifiers, but in Godlycookied we're preparing to seal ourselves off from the sinful and contaminated upper world, so for thematic reasons I'm moving cavern water around and irrigating stone layers instead of farming in soil and tapping the aquifier wherever I want a well.
After the siege was lifted, I sent my citizens out to recover what was left of the caravan. They were about two-thirds done when the leader of the Diomedan pony civilization personally laid siege to us. I sent out a squad of archers to cover the retreat and put the rest of my troops inside the entrance near the trade depot, but one idiot was too busy drinking booze from the caravan (someone else's booze always tastes better than your own) to obey the alert, and I didn't pull the squad back in time to prevent most of them getting cut off. My animal-capture cage traps were insufficient to stop a large siege, and a group of war-trained Diomedan dire spiders came up through the hills behind the entrance, forcing me to seal the gate while the idiot, her child and a few troops were still outside. About half of the spiders got inside and mauled many troops and a few civilians before I managed to put them down.
Outside, my troops put up a decent fight but were eventually dropped and tortured to death. The idiot civilian they were trying to protect survived longest, hiding amongst the trees surrounding the booze she was so busy drinking, but she and her child were eventually caught and killed.
After these disasters, the general mood was poor. Ghosts appeared, frightening a highly-skilled worker to death, and another valuable pony, one Sun Budbrand, was very unhappy. Wax Fruityconvent, a child I was grooming for the militia, went melancholy and three babies died from thirst or hunger. Someone toppled the soapmaker's workshop. Sun Budbrand kept tantruming, and then he loosed a laugh, fell and terrible!
My only butchers' shops were set up in a temporary area underneath the wastewater tank and well away from everything else, so I hit upon a plan to solve two of my problems: Once he claimed a shop, I locked him in, constructed an airlock and arranged to move my melancholy child into it. I unlocked the inside door and natureDwarf Fortress took its course. When Sun Budbrand came back, his mood was much better and he was hauling a really nice pony-bone bed. He said it was called Nightmarestood the Torturous Sun, but was strangely evasive whenever anyone mentioned that missing child.
Two years later the intruders were gone but the SIEGE flag was still there. I noticed that the stocks screen showed a forbidden weapon in a tile containing a tree on the edge of the map, so I eventually had my deforestation team cut it down. When the tree came down, a hostile spearpony who hadn't been on the units list showed up and scared off my haulers. I sent my militia to deal with him, and once they dropped his mount, Wing Dawnspring the Frigid Crab of Princesses decided that using her rainbow whip just wasn't sporting. She one-shotted him with a hoof to the head, bruising the muscle, jamming the skull through the brain and tearing the brain. The SIEGE is now lifted!
While my troops were moving around, Adhabu Ghadhabumchawi the wereiguana (hrosiguana? hroswereiguana, since it was a cave pony turned into a giant iguana twisted into humanoid form?) decided it was a good idea to attack my militia commander, who shot him in the heart and then danced around dodging Adhabu's attacks and insulting his mother as he bled to death.
tl;dr A fell mood solved two problems at once, and some soldiers decided not to put up with any bugged sieges or uppity lycanthropehippoes.