For all you people saying 'The owner was not at fault, it slipped the leash etc, at least he's willing to pay for it to be replaced', wtf is wrong with you people?
The owner is instantly at fault when the dog slips its leash (which all dogs do at some point) and is not immediately brought under control.
I myself own a large dog (rottweiler/boxer cross) and if he ever slips his leash and goes charging after another animal/human (or if he's being walked off his leash, see's something and goes after it) he will drop to the ground straight away as soon as you give him the command.
He knows that if he doesn't drop instantly, he's going to be caught and made to suffer for the rest of the day (just to clarify, being made to suffer involves lying in one spot, getting no attention, food etc. IMO physical punishment should only ever be a last resort).
IMO all dogs should be trained to do this (even if the dogs a tiny little thing that couldn't do much (if any) damage).
Condolences to the OP, I'd be devastated if this happened to me.