I am a huge fan of MPA for conducting certain tasks, but I don't think we are being credible when we think of long range SAR for crashed aircraft as one of them. The chances of anyone surviving such an incident are close to zero, and even if they did it would be unlikely they'd survive long enough in any poor weather long enough for the aircraft to drop a liferaft - personally I doubt they'd survive the longer exposure needed for a recovery vessel to reach them.
Yes we can not send someone out to find the wreckage, but given how rarely aircraft go down in the north atlantic these days, I struggle to justify retaining an ability to tell someone a few hours faster than would otherwise be the case the blatantly obvious statement that their loved one is dead. Sorry to sound blunt but that is what it boils down to.
Finally, and tangentally. I was talking to an ex Nimrod guy the other day who mentioned Royal SAR - when did the RAF stop doing that task?