HI there,
If the timing belt brakes and the engine is an interference engine, you will bend valves in the head as the cam belt brakes the valves will be stationary and the pistons will strike them, now all is not lost,i am yet to replace an engine when a belt brakes, what you will find is that you have bent a few valves which can be repaired, the head will have to come off, and it will cost a few $$$ but i would be very surprised if the engine is damaged beyond a few bent valves. This damage will occur in a micro second with no warning, this is why engine timing belts should be replaced when due.
mark (mhpautos)