You would be able to get away with it in the US domestically, although you might end up on a black list. If a flight is delayed for over three hours (four hours internationally) an airline must let passengers off or face a fine.
I always thought that if a passenger was "missing" cabin crew ask the missing pasenger to identify themselves and having ascertained who is missing see if they have any hold baggage. Hopefully for others on board they won't have. However, I'm not sure how that works for multi-sector flights. In my experience usually everyone is deplaned and reboarded. Perhaps someone can give some real life examples where this is not the case.
What is to stop someone feigning an illness or a panic attack? Again there may be long term repercussions but it would possibly work at the time.
Thread (& fourm) drift:
Historically there were a large number of multi-stage flights - I've done a number in my time but not in this century. Have a look at historical timetables - I've seen nine sector US domestic flights and there are the famous RTW flights such as Pan Am 1/2. You may have had the choice of whether to stay on the plane or get off for some fresh air at stops. Pre 9/11 I've seen parts of terminals at places such as Seattle cordoned off to allow unclearted international pax off the plane (in that case I think it was Eva Air NYC - SEA - TPE).
Also historically you could fly a certain percentage above the great circle route on a standard IATA ticket (I forget the amount, 15 or 30%?) to facilitate stopovers - indeed you could buy a ticket from London to Athens and stop off at three of four European cities en route. This led something called 'hypothetical pointing' where you added the extra mileage after the destination (so bought a ticket tfrom London to Seattle & flew to LAX,etc) and not the last sector. I'm not sure how common this was in the era of 'reputable consolidators' better known as bucket shops. Do standard IATA tickets offering full refunds, transfer between airlines, x% extra mileage & so on still exist these days?