Of course you are in a terrible position, but I agree with the above statement, you cannot help this little puppy, and sometimes, that is just how it is. Take the breeder up on their offer, but get the next puppy double checked by the vet before you agree to take it home and fall in love with it.
You could do worse than get the parents hearts checked also - before you take the puppy home.
wish I could insert a smiley group hug for you, and you are clearly a wonderful dog owner.
Sometimes though, you have to do the hard yards, and this will be one of those times.
regards
HelenB