The problem with that is I don't know what that would be in this world. Not even a wizard with a wand in his hand, because if it's a real threat, it would escalate the story too quickly.
If they were back at their own school, they would know what to do. Perhaps this venture out was a bad plot decision and should be excised. . .
Ah, well, first I will let one of them ponder what they would do, back at their school, and then I will bring in the students who imitiated them but are now leaving their tutors for schools. Then -- we'll see.