If it ever happened on a plane, then it means that the maintenance was intentionally skipped. If they reach 248 days of continuous operation then a number of significant maintenance cycles have been skipped (some 23-25 inspection / maintenance cycles that generally require shutting down the electrical system). The generators in question are attached to the engines. The engines have a overhaul schedule that is shorter than 248 days of continuous operation. If they managed to reach this point, then the major maintenance cycles have been skipped and the engines are long overdue for a tear down inspection and overhaul. Any plane which could reach this point, 248 days of continuous operation missing all of the required maintenance; this is not a plane (or an airline for that matter) which anyone should be flying on.
You would think that if this situation was unlikely to ever happen in practice that the FAA wouldn't have deemed it necessary to issue an AD requiring that the GCUs be power cycled at intervals no longer than 120 days. You'd think they'd already be aware of required maintenance intervals that require powercycling the GCUs, and they waived the usual comment period before issuing the AD due to the perceived imminent danger.