They were strongly suggested to return, as Stainless released concept art of the "new" Stiffshifter. Added to the game in Update 4 (16th July 2014), there's only one Grimm... the other one is hand-puppet. Nobby stated that the other Grimm died between games, and the puppet is a coping mechanism for the bereaved brother. The late Grimm is currently located in the back of the Stiffshifter...