Since FATE's seem so similar to Rift's rifts why not go all the way in copying them? As in if players won't react to some FATE events, the monsters might "spill over" and start conquering parts of the zone. Eventually some hubs might be run over and the players would have to either take them back or wait it out so that the NPC's would spawn back. These invasions of course scale with the amount of players in the area and in some cases escalate to a world boss if/when players fight back.