Refering to the EC 225's FLM, in case of losing one APM; continue the flight (no limitations), in case of losing both APM : Limit duration of flight, leave IMC ASAP. To answer to your query, the only way to leave IMC quickly and safely is to continue the IFR approach, manually. IF your destination is below minimas, apply the normal rules.
Every operator has a MEL based on the Eurocopter MMEL, so the answer about offshore operations is certainly in this document.
Cheers