That would be part of the autopilot. It will probably use a combination of GPS, maps, and radar to avoid this. And it would fly in circles waiting for people to wake up.
Sure, you can come up with a solution to any objection, but the problem is failure modes you haven't thought of. The overall point is that any safety measure brings its own dangers along, and you have to be very careful when adding stuff to make sure that you've solved more problems than you've added. It's not at all obvious.
