I'm sorry, but I also think that chick is too far gone to fix, and most likely was right after the attack.
If it makes you feel better to spend hundreds of dollars on what is most likely going to be the same end, please do so. I understand wanting to try everything you can first, and if a vet visit keeps you from second guessing, that's ok.
If it was mine, I would put it down. That poor thing can't be comfortable and making it suffer isn't right. I had to euthanize a two day old chick this week. Not fun, but it was over fast, and was the right thing to do.