Despite my best efforts, I was unable to keep my crippled mayor happy and he went insane in his hospital bed. In a berserk rage, he killed the 5 other convalescent dwarves in their beds, crippled the chief medical dwarf when he rushed in to check on the commotion, burst out of the hospital and killed a woodcutter with his bare hands before the militia commander was able to stop his rampage.
It seems that the trauma of murdering his old friend was enough to make my militia commander lose it, and he also went mad, and was shortly cut down by his own squadmates. The madness is spreading like a disease as miserable dwarves go berserk, attacking everything in their path. Attempts to get a friendless loner to the emergency bunker were foiled by a rampaging herbalist with an axe and a deathwish. The population of the fortress has dropped by 23 in the last 4 days in game, and all of my legendary dwarves are among the fallen (apart from the Legendary Weaver, and he's nursing a broken arm in a corpse filled hospital, waiting for a dead doctor to heal his wounds.)
FUN fact: 6 dwarves insane, all of them berserk. Never seen that before.
EDIT: Oh god, an armorsmith just got a fell mood, claimed a magma forge and butchered a baby on the anvil. Upon further viewing, her husband was the mayor and the baby she murdered was her only daughter. She has been quite content lately.
EDIT2: She made Desorutheg, "The Entrancing Cancer", a dwarven bone chest. She then quite calmly walked through the swarms of tantruming and insane peasants to go to the quarters she used to share with her husband and daughter, and went to sleep.
In other news, the only bridge out of Standardelbows was toppled, meaning everyone is trapped inside. My milker/cheeser went berserk and murdered my trapped sheep and ducks, as well as a few dwarves who tried to return the fleeing animals to their pasture. And the last dwarf with any combat expertise just went melancholy. It is no longer a question of if, but when.