Indeed, I was thinking destroy the Dementor as a show of force and threaten with challenging Draco to a duel to the death (I'm presuming he can do that as a Noble House). For, I don't know, willingly participating in a travesty of justice against a friend of Harry's or whatever. Close enough to a trial by combat, which also is presumably possible in this "justice" system, so yeah, maybe that after the show of force.

I'm still slightly rooting for Draco to intervene, though. Slightly.

Edit: Oh yeah, that torture thing. Even if Draco has been wiped of it and it's thus unprovable (aside from being not sufficient debt to cancel Hermione's supposed debt), the claim would probably be sufficient grounds for such duel.