Not as tragic, but also somehow incredible story that happened to me today. It should be mentioned before the start that I don't have the best luck with cave ins, although it should be pretty quickly apparent.
Edit: Wow, I almost forgot my actual tragic story. It's after the first paragraph.
I embarked on a mission to undermine and collapse a goblin tower. However, the real target wasn't the tower itself, but the demon leader of the goblin situation, the demon the Age of the world was named after. After a glorious collapse, I checked the units screen to confirm the kill...and I found out that demons can fly. Aww, carp. So, I decided to still kill the demon with a cave in...but a more interesting one. I built a tower to the tallest Z level I could; 25 levels above it. At the top, I built a bridge (which do not support constructions, and are thus good for causing cave ins without effort), and a wall to cave on top of the demon. However, the completer of the project was the current leader of the small 4 dwarf party, nicknamed "Dear Leader". The cave in killed the demon, but Dear Leader also fell to her death. As I saw her corpse lying at the bottom of the ruins of the dark tower, I felt like the tiny smile on the dwarf icon was her smile at completing her mission.
Story 2: the tragic one
So, I was attempting to make some magma forges, and I'd got a room set up, and channels underneath it for the magma...but I messed up on how I made it. I couldn't channel out the magma from above, I'd have to actually have a dwarf mine or carve a fortification to get the magma out. I decided to go with the latter route, and set the jobs up for my 2 channels. The first channel, a child shows up. I shout at the game, cancel the job, but the child comes back to do it again. Apparently, he was a determined little dwarf. He begins carving up the fortification, and the 2nd dwarf shows up for the other channel. It's the hammerer. My mood turns around, as I'd been wanting to get rid of the murderous bastard. However, I'm whiplashed back to horror as the child finishes his fortification...and outruns the magma! I was so happy, it was all going perfectly.
Then, the hammerer decided such work was beneath his noble stature, and left his carving unfinished. Horrified, I watched as the miracle child began to carve again. He was not as lucky the second time.
(Side note: That magma channel had some more interesting times later on. I messed with megabeast size so they'd survive worldgen, but didn't realize I could not undo that. I wound up with a size 200 bronze colossus in my fort, wrecking everything. He punched out the door to the magma channel, and melted his feet. For years and several reclaims, I had a huge lumbering colossus of death that couldn't catch anyone.)