It's a situation that often played out in the movies - the pilots are incapacitated, and the person in the cockpit is looking at all of those instruments and controls, wondering what to do with them.
How much of a chance would this person have? Assume that the person can successfully communicate with Air Traffic Control over the radio.
This is closely related to Can a passenger realistically replace suddenly incapacitated pilots?, but I want to stress that the person in cockpit would have no prior flying experience whatsoever, while the plane has well-functioning autopilot and autoland systems. Can a modern plane be landed without ever touching the throttle and control stick?
P.S. A clarification on why I assume that communication with ground should be realistic. Many commercial planes today have WiFi on board, and people, even if not voice calling, are able to actively use their social media accounts. A video from the cockpit with appropriate commentary will instantly attract many views (and, however perversely, "likes"), so the person who sent it would eventually get in contact with appropriate authorities and get necessary instructions.