Nothing ridiculous about that theory, especially if it's confirmed the plane dropped to 5,000 feet.
You can't just park a 777 in the middle of a jungle and expect it to start right up like nothing happened a couple of weeks later.
No only would they need to find a lot of Jet-A fuel which you can't find at your local gas station but a modern airliner like a 777 require constant maintenance. Also, without proper ground power (which I assume they wouldn't have) you need to use the APUs to start the engines which is possible of course but it adds another layer of complexity on top of everything.
I'm not saying that the theory is impossible, but keep in mind that a 777 is not like a car that you can simply fill up the tank and turn the key to go.
Also how is the fact that it dropped to 5000 feets makes it easier? If anything it would actually makes things harder because flying at 5000 feets wastes a lot more fuel than flying at cruise altitude.