I think they are pretty much done. I think Angel Exterminatus was supposed to be their great book. They were pretty brutalized in my opinion. Maybe we will see them at Terra? But as far as a novel contribution, I think they join a couple others in a disastrous finish.
That's a real shame...Have yet to read Angel Exterminatus but one of my fav Legions and Primarchs...and all they get is a cameo in Battle of Phall where they look like incompetent fools (even with the attack lead by the Perturabo!). I think this Primarch needs at least a novella to open him up. Other Primarchs got so much more attention!