What action should a pilot take during a loss of communications when under IMC?

In the event of a loss of communications while operating in Instrument Meteorological Conditions (IMC), the pilot should follow the last clearance received from Air Traffic Control. This action is appropriate because it allows the pilot to maintain a safe and compliant flight path. By adhering to the last instructions given, the pilot can remain aware of any traffic control measures that were in place and ensure that they are not entering controlled airspace without proper authority.

Following the last clearance helps in avoiding potential conflicts with other aircraft and ensures that the flight continues in an organized manner within the air traffic system. Additionally, the pilot can proceed to the next expected fix, route, or altitude as indicated in that clearance, thereby maintaining situational awareness and safety.

It's important to understand that simply continuing to the destination without deviation, returning to the departure airport, or engaging the autopilot and awaiting communication do not provide the same level of adherence to safety regulations and situational control. Each of those options could result in entering restricted airspace, creating confusion for ATC, or potentially endangering the safety of the flight and others. Thus, following the last clearance received stands as the most responsible and safety-conscious action to take in this scenario.