Isibel hugs him as hard as she can, which isn't very hard really. He should be invisible when he sleeps, perhaps, or he could disguise himself as something other than a demon - aren't they supposed to be able to do that? - and accompany them. She'll be awake, soon enough she'll be a competent Elfmage, a Sarion, and then she'll need to go - wherever she needs to go to stop the darkness, and not even elfmagery will let her fly without someone to carry her. (This may be a flaw in the sleeping plan, at least if there is any intention of implementing it before the danger is past.)