Remember that all modern mag ignitions are now breakerless (no points). This means that many times the mag source coil, either integral with the HV coil or separate in the case of Zenoah ignitions has an internal circuit that can fail. These coils are more of a module than just a coil of wire. So yes, they can and do fail. I've had lawn equipment work perfectly one day then be unable to start with no spark the next. Replace the coil and they were good to go again.