Way back in the late 70s, as a kid I was on flight from LHR to DAC, with a stop I believe in DOH. For the vast majority of the flight in a 707 I was in the cockpit - initially in the RH seat. When the captain went to take a break, the right seat was taken back by the SO, and I moved into the LH seat.
At some point in the flight, with the captain still out, both the FO and the FE left the cockpit - leaving me in the LH seat alone in the cockpit...
Go figure - plane still got to the intended destination, and nobody was fired, or a big deal made of it - although they probably should have in that case...
I was pretty well versed in the theory of flight at the time, and had a good understanding of what the instruments and controls were there for, and how they worked. Not to mention that I was not able to reach the rudder pedals and any other controls at the same time in any case...