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

Citing Dr. Hess (sp?) as them killing main antagonists isn't the best example considering her lack of popularity in comparison to Lucifer's. As far as Crowley goes, it's pretty common knowledge now that a variety of factors contributed to him leaving the show and very few of them had to do with story-feasibility. With that said, I do think it's a possibility they will kill him off, however here is what I think will or hope will happen: Lucifer chooses to stay in the alternate reality. I can see this being a logical plot device for a variety of reasons most of which is that it is very much like the world he would create if he could. We never really got to see Crowley come full circle, which for me would entail the Winchesters really acknowledging that there is some sort of feeling there for him. While we're not likely to see that happen with Lucifer, I don't think killing him or locking him away would give fans the proper closure they need.