Another possible reason Asmodeus left Ketch could be because he was high? How many hits of Archangel grace did he shoot himself up with? Two? Three? We can hope if it was a trick that Asmos plans fail as often as Fred’s do... :)
Of course that is also a valid possibility. They did play with the Crowley parallels and his human blood addiction very deliberately, so it could absolutely be the case. Maybe we’ll get a scene of him in another episode, but... and yes, maybe I am expecting to much of Dabb and Co. lol the whole scenario of Ketch catching Aesmodeus shooting up and himletting the vials laying about when not in the room... There are just a whole lot of blanks left in that scene. Which is of course nothing new with SPN, but I hope with this one there is more to it.
In any case we can assume that the angel grace must have done something to Aesmodeus as he did appear much more focused on emotional burdences and redemption, which seems utterly ill-fitting to how and what we have seen of him prior, so maybe like with Crowley when he became more human and he started to talk about forgiveness, maybe the angel grace did spark some hidden emotion within Aesmodeus as well. His entire quote
“You want redemption, but you are never going to get it. Your kind, our kind, we can’t be redeemed. All we can do is spread our pain around. So no, you don’t know who you are. But I do. Which is why no matter where you go, no matter what you do: you’re mine.”
felt very omnious and alluding to for what’s to come.