Might be one for a current 747 pilot to answer - in the mean time obviously (?) the 747 Fleet is seeing a gradual reduction in “plum” destinations but it has still got some good ones. One even ended up in SIN last month as “sub” for the 380!!!!
OTOH all the Longhaul Fleets are seeing some uncertainty and last minute plan changes due to the 787 engine issue.
As for Longhaul life at BA in general - TBH I am increasingly of the opinion that many will find the model BA seem to be aiming for and one which BALPA seem to less and less able to moderate will be one that is unsustainable over a full time, multi decade career. A single person with minimal commitments outside work who additionally never gets a cold or flu might manage.....for mere mortals with families, especially young ones I have my doubts.