There is nothing you can do. They aren't even on your lease - I bet your landlord could evict you for even having them there based on your lease said when you signed it. This is why its never a good idea to let people just stay with you with nothing in writing - they aren't on the lease- legally they aren't responsible for damage to the apartment.
If they were really good friends and you had to pay for it I"m sure that they would offer to cover it - but based on what you wrote about them I wouldn't hold my breath on that happening if I was you.