Perfect world (flaps and gear up too), the answer would be until the aircraft fly's its self into the ground for most modern airliners as it fly's into the programmed STAR and there is no one there to lower the gear and flaps and arm autoland, may just run out of fuel. Depends on type.
Could have a very long card game and get soo !!!!faced they pass out for the big show.
Perfect world assuming they don't get shot down as well.