Well in Texas you can get terminated without cause at any time (and by the same note you can leave at any time), so he doesn't have a case there.
The issue will be that when a prospective employer calls to verify employment and one of the few questions that are allowed is asked "would you hire them again?" and they say no. That's a huge red flag.
In any case, my brother does work for a couple companies that do rigging and lighting for concerts (House of Blues, the new Cowboys stadium, etc.). They *might* be hiring, but I don't talk to my brother much so I can't get you a good lead as to who to talk to. Maybe call the HoB and see who does their setup and tear down?