As the safety director of a construction company, I can tell you that right at this moment, somewhere in the greater New Orleans area, the panicked owner of a roofing contractor is on his knees praying to God that you don't file a lawsuit, and that OSHA never hears about this incident.
As far as firing the crew? That's a given. There's no excuse for losing control of materials like that, and there's definitely no excuse for failing to control access immediately under the work area. (and no, a single strip of barricade tape is not adequate control)
Hell, I'm irritated just thinking about how sloppy that was.