On flights of less than eight hours there would only be two pilots. In a real world airline, you would usually have a pilot or two deadheading internationally.
Still, the widebody single pilot scenario has happened occasionally from what I understand. I've been told of an incident at a cargo airline where the FO became miffed over the captain's instructions and refused to even operate the flaps and gear into NRT. And, a lot of Asian and Middle Eastern airlines fly with very low time ab initio FO's. No problem for the captain, he's used to doing it solo but the question of whether the FO could really land alone has been raised here often in the past.
In the U.S. we're supposed to wear a mask if only one of the pilots is left on the flight deck at altitude in case of rapid decompression. However, working overseas, the lone pilot was also supposed to lock his shoulder harness in case he passed out to avoid the slump over the controls depicted in the movie 'Airplane!'