Update - He promised me he is getting rid of his dog ASAP, he said he'd rather find it a home but if it comes down to it he'll put him down.
My dog is going to the Vet today at 5:30 pm and he's picking up the bill.
I'm pretty sure that if I had shot his dog it would've turned much uglier as the cops would have come, he would have gone to jail, and my dog would have been labeled a people biter even given these extreme circumstances.
Given the situation I think it's going to turn out OK as his dog is going somewhere, my vet bills will be taken care of, and most importanly I'm not going to lose a good friend...