I would be sick about it too and sorry that happened. Take comfort that they didn't mean for that to happen. It's not like they took it out to the yard for the kids to play with and then left it for the dog.
It was an unforseen accident and they too are sorry it happened. I would repair it and give it back. It might take years for that to get done but if it is not repaired and is still being used it's not going to last as long as it could.