I am also a part of the club that isn't particularly worried by Cas' fate next week since we know he is going to be in episodes 15 and 19 after this. However, while we are on the subject, I am worried about his fate later in the season for several reasons. Firstly, last weeks episode was the first truly Castiel centred episode since season six and now we are suddenly getting another two in the same season. As a Castiel fan, this seems a little too good to be true and an unusual turn of events, and I am worried they're treating us to a large dose of Cas in order to give him a proper goodbye in his final season. Secondly, one of the key themes of Lily Saunders has Regrets is that Dean and Sam are more important to the world than Cas and he is willing to make sacrifices in order to ensure they survive. It can be argued that this is setting the stage for Castiel to sacrifice himself later in the season in order to ensure Sam and Dean stay alive. Thirdly, spoilers have revealed that episode nineteen will "focus on Cas in a way the first two haven't". Unless they're going to make it an episode purely devoted to Cas with Sam and Dean in one or two scenes just I really can't see how they intend to do this other than making it a Death's Door type episode.
Also I've never understood the complaints Castiel or any other character are 'overshadowing the brothers'. They're in every single episode. Castiel, Crowley and the other recurring character are in half the seasons episodes at best. So Sam and Dean are still the main focus of the show.