Not exactly. If some schedule complication occurs, the passenger would have to get him or herself reaccommodated immediately by the airline.

Let's say that a connection is missed because of a delay. You can't just walk away from the rest of itinerary and expect your return leg to still be valid.

Finally, if by "schedule complication" you mean something like the passenger couldn't make it to the airport on time because of an "accident on the highway" (wink, wink, nudge, nudge), the same principle applies.

The passenger has an obligation to contact the airline immediately to be reaccommodated in the most convenient possible fashion,

Just because there might have been a delay getting to the airport, doesn't mean the airline will just forget about one of the legs on your itinerary.

Finally, as was stated earlier, you can get away with missing your final leg, but try this more than once or twice and you risk being banned from flying the airline again, or at least being removed from the rolls of their ff program.