User blog comment:Tommy,Klaus&Kol2012+/mistakes in supernatural/@comment-26992577-20150917133317

Sam and Dean are in some way unkillable, as one of the brothers can always call Castiel and resurect the other. This was especially true during season 6 when Castiel was so powerful, he could just prevent Dean from becoming a monster be touching his shoulder.

I hope The Darkness can kill humans or anything else permanently, means if Amara kills somebody, she destroys their soul as well and their is no way to ever bring that person/ being back.