User blog comment:KillRoy231/Mary and Lucifer to return/@comment-69.129.120.213-20170623103015/@comment-1031724-20170625182021

So they can kill main villains that aren't very popular (Hess was a lot like Umbridge), unless they're reformed, then the more popular, the lower their chances of survival. Metatron was killed like two episodes into his redemption. Crowley lasted the longest and used to be on the line they couldn't cross along with Castiel, but you say there were reasons he left the show.