At the moment, I`m rolling ideas around, including a great endeavour for my players, where they might find traces of a lost chapter of second founding Space Marines, that lost all it`s warp-capable ships.
Maybe they conquered a small Imperium made up from one large star system with many planets and asteroids and believe, the greater Imperium has been destroyed by an outer threat like chaos or the hive-fleets.
So now the job of the pc could be to re-establish contact with these worlds and these marines, to bring them back into the fold of the Imperium of Mankind.
ideas, comments?