I hope if medication or a vet's assistance isn't available that a much more humane method than a hammer would be used. It would be disturbing enough without crushing a puppy's head.
I understand not being able to tolerant a crying/screaming in pain pup, but I know hitting it is just something I could never ever do. I think better "restort only" options would be placing a pillow over it's head or drowning, as awful as those thoughts are too.
Personally, if I were to breed, I'd make the necessary arrangements to prevent such a last resort scenario, including any additional costs of having "someone" on call without necessarily needing their services.
This thread makes me very sad......