Even if the pilots didn't, ATC would (and the plane's own GPS unit's internal checks might notice as well) - and then it's simple enough to disable GPS and use VOR navigation (or radar vectors, in a pinch).
Couldn't the same thing happen with a drone? After all they are being controlled by someone one the ground. If you notice it behaving erratically or ATC notices and contacts you about it you could correct the issue. In fact that is exactly what happened in this situation the drone's autopilot was overridden by another pilot to prevent it from crashing.