If an en-route IFR aircraft suffers a complete radio communication failure while operating in IMC, what standard procedure must the pilot follow regarding their route and altitude?

1. Maintain the last assigned route and altitude (or minimum flight altitude if higher) to the designated holding fix, then commence descent at the estimated time of arrival (ETA).
2. Immediately descend to the lowest published VFR altitude and fly directly to the nearest uncontrolled airport.
3. Maintain altitude and route, but immediately divert to the departure airport using a 180-degree turn.
4. Climb to the maximum service ceiling of the aircraft to remain clear of all other traffic.