If you have reconnected the senor/s and there is no fault with it then the light will go out after 3 drive cycles, this is a legislated requirement. A drive cycle refers to an engine warm-up from say 25degC to normal op. temp. Just switching off and restarting is not a warm-up. The rear sensor (post cat) is used to diagnose a failed cat. It will not affect the performance of the vehicle and you disconnect it for good if you like, but the MIL light will always be on.