Graham, I am so sorry that you had to experience this horror. I hope that the idiots responsible do learn their lesson and I hope that you get as much as you can from them. People like this only understand the value of money.
If they have broken law by entering your land with a firearm then they certainly need reporting to the police. They should also be paying, not only for the goat and potential kids, but the cost of the vet if he/she attended. And for your distress - not that there's any amount can make up for that. I would also want recompense for the loss of milk. Of course your poor girls are upset and it's bound to affect their yield.
Most of all, I hope that you can be at peace about it all, in time.