Yes, wolf packs are leaving because contrary to popular belief Destiny does in fact have a story. And due to the nature of that story, it progresses. Just as the blades of Crota left once Crota's invasion was thwarted, so to will the wolves now that their rebellion has been crushed. Once TTK drop, the events of HoW will be in the past. So, lore-wise, all the Fallen hunted will be dead once TTK comes. It doesn't matter if [b][i]you[/i][/b] did it, lore-wise, [b][i]someone[/i][/b] did.