1991 Mazda 2.2 liter engine cam pulley bolt broke off?

My neighbors car stalled at red light, A 1991 ford probe. They ran the battery down trying to restart. They told me they tried to push start the car and it would not start. I charged the battery, tried starting fluid , then I pulled the coil wire and no spark. Then I pulled distributor cap and found it not turning and that led me to pull the timing belt cover and I found the problem. I'm not familiar with this engine, and I'm wondering if someone knows, if valves or piston damage is a sure thing ? Is the engine salvageable? I haven't seen this with anything I have worked on before, so why this bolt broke is a mystery. Should I tell them look for another car or used engine? I'm looking for somebody that knows this particular engine characteristics.