It doesn't return to ground. The earth is part of our electrical system only because we choose to connect the system to it for safety reasons, but it has nothing to do with the "flow" of electrons in a circuit. In any circuit, the electrons don't flow, contrary to popular belief. They wiggle back and forth. The electromagnetic field around the conductor races forward and does the work. The electrons stay put. Otherwise we would eventually run out of electrons. BTW, before you tell me what an idiot I am, be aware that many textbooks are wrong.