I hope that Slad just leaves him there. It's a better fate than he deserves, but at the very least that bastard won't be able to hurt anyone anymore.
Also, I can't help but like this fairy. She seems like a real sweetie - she just wants people to be happy. And her being all excited that she actually gets to talk to and directly interact with Slad just makes her so adorable.
I kinda wish that he can convince her to be a companion for their party. But it'd almost be too perfect because anytime they need to rest and recover while dungeon diving, BOOM! Instant safe house, with all the food and comfort they need to rest and fully recover. (After all, she said that her dreams effect their bodies exactly as if in real life.)
It would also be kinda cute if it turns out this fairy is a sort of other-worldly hikikomori who is, for some reason, utterly afraid of going "outside", so instead she experiences the outside world vicariously through the people she traps. Though we might be in for a bit of tragedy if this trope is not only employed, but also deconstructed.