The puncuntured lung sounds like it can be recovered from. But how serious is the broken back? will the cat be paralyzed? I've only lost 2 pets (not gonna count the fish) My little dog "Tika" was hit by a car. Her hip was shattered, both legs broken & internal bleeding. We where faced with the choice of trying to save her or putting her down. Sadly we had to put her down because the vet wanted a large sum up front before he would attempt to save her, and we were broke. That was a very hard thing to do. Looking back is difficult now because we are better off financially and can afford to pay that kind of bill. More recently I lost my cat to a fire that also destroyed almost everything I owned. That was actually easier to take. It wasn't my decision to make, and I couldn't blame myself. Don't know if this will help you any, nor can I give you any advice on what to do. Good luck