The Mark is just as much soul-deep as skin-deep. I know they did manage to remove it the first time, but I didn't particularly pay too much attention to the how of it. It was too much of an annoyance for him, and besides, he was free from his Cage again and snug into a "new" vessel. Mark was gone, they had other things to deal with.

I mean, we'll either figure it out, or Dean kills everyone in Free Cities and keeps on trekking. I think throwing him at the Singularity outside of the Dimming could be a fun experiment, but I suppose that would keep you from getting your Best Friends Forever bracelet from your rock.

But it might be the only way to really kill him, Lucifer's just not sure how to get Dean there.

"You should make Strange do Rhy's next banquet. You'll still be recovering from this, after all."

He's only mostly joking... about both comments.