How very sad,for you and the pup
Were I in that situation,I would probably need to do something,would not be able to,just get on with my life.
It sounds like a horror story IMO and I would want some kind of justice for my dog,even if it means the vet will only be reprimanded.
It could be he has more complaints,this should be reported to the Vet-Board,if it were a human patient,there would be no question about what to do,a little dog should be no different.
I am very sorry this happened to your family