Armok giveth and Armok taketh away.
I had one majorly distraught fortress, but it was mostly my fault.
I was digging out rooms for magma pumps. The first set of pump stations were not to my satisfaction so I designated a second set. While I was waiting for the pump parts to be built, I designated that certain parts of the first set of pump stations be modified for other uses. While my dwarves were mining, there were at least two cave-ins and two dwarves who ended up in the magma pool at the bottom the tunnel. I called it quits on the modifications before anymore were lost.
Next, I made a prototype perpetual water pump with two water wheels above ground by the main stream. I forgot to add a fail safe, and, of course, the bloody thing overflowed. I designated the whole contraption to be deconstructed, but no one could reach the the pump or the water wheels. Over the course of a few months water reached the foot of the bridge at the entrance of my trade depot's fortification. One of the merchant caravans had trouble crossing to get into the depot's fortification. So I got fed up and, like a New Deal work program, I had my dwarves work to channel a massive reservoir pit. Then, I had them channel some of the water away from the source of the pump system. Because they were dwarves, some of them arbitrarily channeled all around themselves and below. At least two of them drowned, never to be recovered from the channels but well within plain site.
Later on, I built a military to deal with all the guests from the caverns and elsewhere. They were all noobs, and, to be fair, so was I at the time. Well one day, some rutherers came up to greet the dwarves. All my dwarves went to dispatch the beasties as I ordered, but not a one of them took a weapon. I had ten unarmed dwarves fighting two rutherers to the point of exhaustion (granted part of the squad killed another rutherer in the tunnels). Then, cave crocodile came and killed three of the conscious recruits. I decided to abandon the fort before any other tragedies befell the fort.
The moral of the story is that memorial slabs are the kindest gift Armok has granted dwarvenkind.