Depends on the person, major business risk to a Flight Training School, not in any particular order, losing aircraft (taken offline), losing staff (at the drop of a hat, not the young ones that you're mentoring and know are going to leave) and poor or incompetent service.
I've had two airline pilots (approaching retirement) approach me for work. Would have taken them immediately if I'd had the work for them. For a couple of reasons, they were both active in GA throughout their airline career, they were both top blokes who didn't bring an airline ego into the school and they both lived local, were staying put and weren't going to shoot through at the drop of a hat.