My dog was attacked by a bull mastiff tonight and literally his leg was ripped off..?

The neighbor's mastiff charges the fence, so the neighbor put a brick down but tonight it pulled down a piece of fence, grabbed my dog's leg and tried to pull it through. My dogs leg was mangled and the vet will have to amputate. I called the police and have filed a report, but I'm wondering if there's any hope to get at the very least the vet bills taken care of, which will total around $2,000. I'd like to have the dog removed from the house, considering I have a 5 year old and he charges the fence and obviously can rip it down, but from what I understand the first attack is usually a warning. What gets me is they have this huge dog run kennel in the back yard with a top, so they must know he's dangerous, yet it wasn't in there. What should I do at this point that I haven't already?