Looks to me like it can be fixed; the question simply comes down to whether or not it'd be a worthwhile activity. I doubt it'd be economical to pay someone to do the work, and if you knew someone who could do the work for free, then I doubt that this sort of screw-up would have occurred in the first place.
While the following advice won't help the OP in the least, I offer it up to anyone who may come across this thread in the future - barrel nuts are cheap, pretty damn easy to cut off with a rotary tool and some due care, and are far less expensive to replace than a receiver. I've learned that if I can't immediately crack loose the nut on a factory-installed barrel, then it's best just to cut off the nut and prevent any further waste of time.
