Yes I was thinking the same thing that "morganslady", I love Catiel and I really love Misha but I don't know how its going to fit Misha in the new season, if we want a really good season 6, and Sera already said that its not going to be an Apocalypse anymore.
I think the writers are not going to say because they could spoiled the story. But I think they are going to say that maybe Cas could do a few appareances in season 6, they always say: in supernatural anyone could back.