While it's very clear that a 747 cannot fly properly with the failure of three engines, we can see that a single functioning engine would at least extend the aircraft's distance and prolong its time in the air. Hopefully, this would buy enough time and distance for the 747 to reach a suitable landing spot.

While the Boeing 747 is an incredibly robust aircraft designed with four engines for maximum redundancy, it cannot sustain level flight or gain altitude on just a single engine. If three engines were to fail, a single functioning engine would not provide enough thrust to overcome the massive drag and weight of the "Queen of the Skies." In such an extreme emergency, the remaining engine would primarily serve to extend the aircraft's glide distance and provide critical hydraulic and electrical power to the cockpit controls, allowing the pilots to better manage a forced landing or ditching. Historically, there have been famous cases of quadruple engine failures (like British Airways Flight 9 in 1982 due to volcanic ash) where the plane successfully glided for many miles before engines could be restarted. Modern aviation safety regulations, such as ETOPS, focus on twin-engine planes, but the 747's four-engine design was intended so that it could safely continue a journey or reach a distant diversion airport even if one or two engines failed. However, "running on one" is strictly a descent-management scenario rather than a viable way to fly.