The ever present Chaos Dwarfs

OK; I would assume that this is either a bug or an oversight, but seriously - what's up with the Chaos Dwarfs? As far as I can tell it seems that there's no way to destroy them. Taking over all of their settlements doesn't destroy them, and neither does killing all their units. I tested this during the first turn of a fresh campaign: first make Chaos Dwarfs lose all their settlements with surrender_regions console command, then kill all the evicted units - guess what? - nothing happens. Don't get me wrong, it's not like this is a game breaking issue or anything, but it's just a bit distracting to see the Chaos Dwarf's up on the charts when they don't really exist anymore (I've been playing a really long campaign with Reikland for quite some time now, and it confused the hell out of me; "Haven't I destroyed these guys - settlements taken over and everyone killed?").