MacGregor,
I'm real sorry to hear about your dad's misfortune. Is he going to pursue the contractor legally? I have had my fair share of people stiff me for money, usually after the completion of the job, but never to that degree. It's amazing that people can sleep at night with some of the things that they're doing to others.
I've worked around masonry of one form or another since I was old enough to go to work with my grandfather and pick up brick and block scrap for five dollars a day. At the time I was just raking in the doe!! More than giving me a sense of earning what I got, I was able to see one of the hardest working and honest men that I've ever known create art out of nothing. I thank God that I had him to teach me masonry work but more so work and life ethics.
I really hope that your dad gets compensated for his work. Stone work is literally an art and some of the hardest physical work a person could devote themselves to.