@Shonai_Dweller: I said "not working that well" rather than "not working". Everything just breaking down gradually with nothing built up to fill the void isn't working that well in my book. You'll end up with a world without any civs and a lot of independent sites, which I suspect means all action above the level of individuals just go to a standstill. There can't be any wars if there are no entities to wage them, no settling if there are no entities to send out settlers (as I assume individuals won't organize that), and no reclaims for the same reason (although elves seem to lack the ability to reclaim their sites already during world gen). Sure, my fortress still received an elven caravan every year, even though the elven civ that presumably sent it ceased to exist a long time ago. The goblin site that send sieges became unowned, owned by another goblin civ, and then unowned again, but still managed to send meager sieges at me from the goblin civ that no longer controlled the site (and Legends Mode info claimed it was still that civ sending the siege, even when the site was controlled by a different goblin civ).
Wars, occupation, reclaim, revolution, etc. are fine when they happen at a normal time scale, rather than kicked off in one big mess for 14 days to screw up the world you embark in, only to peter out afterwards. Sure, something must have happened for one goblin civ to claim a site that another civ lost, but then they just sit there as civs' sites break away, without recapturing them or new entities forming from breakaway factions. Thus, there's a fair bit of room for improvement to make it interesting (obviously, the current fortress mode restriction of a single permanent civ per race as the civs you can have relations with doesn't work that well after the world has been activated. I assume that's one of the things that will eventually be updated).