however, whether it would be desirable to do so is entirely another matter
Agreed... but for what reason would you divert? What is the hazard? What is to be gained?
would seem rather more sensible than to carry on all the way across the GCFA and North Atlantic on 3?
I am not trying to pick an argument, but why "more sensible"?
As I did, please try to stand back and look at the situation. The aircraft is safely airborne on 3, all 3 are as serviceable as they were on departure. Emotionally "we have lost an engine". But practically we have loads of redundancy left, make contingency plans based on a further problem.. and decide on that basis (I am talking generically here, may or may not apply to the MRU case).
NoD