I had a post a few months back on what it took to straighten a TF barn door that was severely bent above the belt line. I've been meaning to go back and update the post as there was a lot more work after the initial success. Guess I'll have to stop working on the burb long enough to tell the whole story. The lesson I learned (with a lot of help from the Bolt) is that any door can be salvaged.
"unrestoreable" means you have to either spend money or develop new skills and a lot of patience. The Bolt is real good at helping you with the skills piece. Hammer and dolly can do a lot but when they aren't enough, a cut-off wheel and mig welder work wonders.