This just in, via GameSpy’s latest ArenaNet interview:
GameSpy: How persistent are the game’s dynamic events? To use one of your common examples, if a bunch of raiders wreck a village, and nobody saves it, what happens next? Do players have to group up and retake it by force, or do the raiders eventually “reset” and leave the village on their own, or what?
Eric Flannum: Events are fully persistent. In the example you give, the raiders will never reset on their own, unless players intervene.
To address the inevitable comparison with Rift, which made a change to how invasions worked during beta since they tended to lay waste to quest hubs (to mixed reactions by the player base), dynamic events in GW2 are the content, so there is no argument to be made that a town taken over by raiders hampers content access.
I do enjoy how the confirmations of game systems trickle in by bits and pieces.