User blog comment:IamJakuhoRaikoben/Chapter 333: Man and Man, Dragon and Dragon, Man and Dragon, Review./@comment-4999650-20130531144008/@comment-7418318-20130531145959

Maybe his body was close to death, but when Rogue killed him he didn't just pass his powers, but also his consiousness into Rogue and has been living in some dark corner of the Dragon Slayers mind since then.

Maybe he intends to hide and relegate himself to small manipulations and short take overs (like in the fight with Gajeel) untill Acnalogia is defeated, at which point he plans to push out Rogues mind and take over completely.