Oxygen must be replenished otherwise electron transport cannot proceed.
Each carrier, once reduced, would have to stay that way because there would be no place for the electrons to go. The need to deliver oxygen to the electron transport system is why we have respiratory and circulatory systems. Oxygen is necessary to "drain" electrons from the system, otherwise all of the carriers would remain reduced and electron transport would have to stop. As electrons are transferred from carrier to carrier, the total amount of free energy drops. Each carrier is more electronegative than the carrier "upstream." Much of the energy is lost as heat, but a significant amount is stored in the form of a proton gradient.