Well, I didn't so much kill him, as I failed to prevent 20 goblins from executing him in an arrow barrage and dumping his body in the river. It even caused him to haunt my fortress. None of my dwarfs really cared, but anyway...
Because of his death, I was never awarded a barony (since the guy doing the awarding was now a pissed off spectre). That in itself is fine, but the following year I was then immediately promoted to Mountainhome, skipping all other noble promotions. That in itself is fine, too. But a bigger problem is that I didn't receive a monarch. I got his entourage, but no monarch.
Even that in itself is fine, but the biggest problem of them all is that the nearby goblin civilization seems to be ignoring me. I have over 5 million in wealth but neither mega beasts nor goblins seem interested in taking it. For about two years I had a large ambush every spring and autumn (coinciding with the caravans), as well as the occasional mega beast. But ever since mountain homeage, this fortress is boooooooooooring. Sometimes a vulture flies by, but that ends pretty quick once 50 marksdwarfs simultaneously volley it.
I did recently pass into the Age of Legends, so that might account for the lack of excitement. Also, the neary goblin civilization is rather puny. Only one noble and he's simply called "administrator."
It's been about 2 years since mountain home status. I think the fort was around for 2 or 3 years before that. Did the outpost liason death doom my fortress to boring peace and quiet? Maybe my fortress wealth isn't being properly accounted for by surrounding entities? Or am I just impatient and this is all pretty normal for a fort? I'm starting to get really bored, and tempted to mine into HFS. But that isn't so much exciting as it is surrendering.