a neat addition to dwarf fortress would be for ores that would normally be radioactive, like pitchblende, to actually be radioactive and can give your dwarves cancer when mined from inhaling their dust.
imagine Urist Mcdwarf has a happy family, plenty of respect in the fortress, and loads of experience making him a legendary miner you have obviously grown attached to and would do anything to keep from falling into lava. one day he was digging very deep and hit a cluster of pitchblende. some dust is launched into the air and Urist thinks nothing of it at first. the next day he starts feeling pain, fatigue, and his cough isn't getting any better. he visits the infirmary for a checkup and is diagnosed with advanced lung cancer and leukemia. the chief medical dwarf and 2 others perform and experimental surgery to cut out the tumor in Urist's left lung. you continue ordering your dwarves to do other things like finishing that lava moat and completing turtle shell crafts for the next elven caravan but you always glance back at status of the operation worryingly. eventually the surgery was, to your great relief, a success but there was no way to cure his leukemia. his health degrades slowly over the course of a month to the point where he can no longer stand. he rests on his death bed surrounded by his family, friends of the fortress, and yourself nearly crying manly tears of farewell. his final words were to his son, Urist McJr just before his eyes closed and his soul taken by Armok. the other dwarves begin a downward spiral of depression greater than a simpler death since Urist's was so slow and tormenting. the fortress then falls to tantrum spirals and chaos but is brought back after happy thoughts and memories came to them from the sight and memories of Urist from his grand tomb.
slower deaths should cause dwarves to feel worse thoughts than a simple death since they constantly visit them depending on how close they were when they were healthy. this would add a great deal of feel and fun to the game's already amazing randomly generated story gameplay. when playing legends mode you can read about how an epic hero slowly succumbs to cancer and dies with his friend giving you a real tearjerker.