I dont know yorkiek9, I've not heard of a 72 hour law (not saying it does not exist). In that case if you left your pet with anyone to care for (vacation or what not) would that entitle them to keep your pet?
I don't think he should get her either, but she may not have choice and him having all of the paper work stating that she belongs to him would make a difference otherwise. Having something in writing would simply prevent him from being able to call the authorities on her and them forcing her to give up the dog.
I really think I would take the chance of taking her to another vet while I had her and spaying her and let him just be mad. You have paid to save her life and to breed her again would put her in that same position
, if you call and give the situation to the local shelter see what they say and if they would do it, (you could always say she got out and got picked up and they would not release her without her being spayed) I know that is dishonest, but it may save her life. I would have a hard time giving her back to him though.