Okay, I was thinking about this after a married woodcutter died to some goblin ambushers. I didn't see this suggestion on the dev page, and figured I'd post it.
As far as I can tell right now, if a dwarf dies to a roving beast or a goblin invader, the killer usually gets a name if it didn't have one already, and everyone close to the victim gets bad thoughts. Right. Cool.
But what if what of those kindred dwarfs is an obsessive, moody, impulsive and violent fella? He might go so far as to swear vengeance on the killer, rather than going berserk on other dwarves! It seems like named critters and noble goblins at least, are specially tracked by the game. Now, I don't know the internal workings of the engine, but could they be specially marked out for that dwarf?
It could be almost like a fey mood - He drops his current tasks, grabs or learns to build a weapon and some armor, trains himself to a point where he thinks he can win, and ventures off to fight his hated foe to the death next time he shows up. He could even run off the map after him, and either return victorious with some grisly trophy, or you could hear tell of his death in battle - the first giving the bereaved kin a happy thought, and the second possibly leading to an even bigger blood feud.
You could even implement this for those buggers that deal out serious wounds and escape intact:
Urith Fieldswells, One-Legged Fisherdwarf: "Aye laddie, I lain on this pier with me crossbow most every day since Obsidian. I waits fer Moby-Dick, the zombie whale what took me beard! One day he and I, we'll meet: Either way, Armok gets his present, but me? I'm aimin' to own a masterfully crafted ==<whale>==!"
