It's not an impossible thing, Thorne is fickle in general. The Queen is unstable. Who knows how long she'll see them as valuable. But for now, they are. For now, no eels, but it isn't that he is blindly believing they're safe. Nothing about this place is safe, which he's been saying since the beginning.

"What? I'm just checking. You may have decided you'd rather do this alone."

Lucifer can be very independent and this was a place he went by himself to let loose. Istredd likes being in his space and included in the things that he enjoys, but he was willing to give him an out here. He's maybe always a little concerned that he's too smothering, everywhere on top of Lucifer. He still has his moments of uncertainty, don't look at him.

They are closer to the border so Istredd sets the corpse down and does pointedly look away from what's about to happen. To keep watch, yes, but also because for the other reason.