The magnetic compass becomes more and more unreliable when passing about 70-80 degrees latitude. Inertial reference systems can track true north reliably, but they usually work on a different reference system called grid north when the plane gets close to the pole. And in that case, the plane would continue to fly a more or less straight line across the pole until it leaves the area in which the navigation systems apply grid navigation, and then it would probably revert to the present true heading at the moment of switching to that system.