Now that the Horus Heresy has covered Prospero, Calth, Signus Prime, the Dark Angels schism and Isstvaan (though it's still bogged down there, looking at you Vulkan) I can't think of any more major engagements they need to cover. Anyone got any speculation on where the series is going? And whether we'll ever reach Terra?
EDIT: I suppose there's Tallarn but it looks like that's just a novella treatment.