§ 135.101 Second in command required under IFR.
Except as provided in § 135.105, no person may operate an aircraft carrying passengers under IFR unless there is a second in command in the aircraft.
Regardless of weather the aircraft is approved for single pilot operations or not, or weather the company is approved for single pilot with autopilot in lieu of a SIC, under 135, the company always has the option of using the SIC (if the SIC is qualified) instead of the autopilot, under 135.101, if the flight is conducted under IFR.
To answer your question, if a company has a single pilot authorization they don't need the SIC. However, at any time, they may use the SIC because 135 always requires and permits it, even when granted a single pilot with autopilot authorization. It's part of the basic regulation. Even if the autopilot is working, if the company has a trained SIC and wishes to use the SIC instead of flying the aircraft single pilot with autopilot, the company may elect to do so.
This is just as true in a Cessna 210 as any other aircraft.