Interesting thread.
I have no problem with a big 4-jet continuing following an engine loss, as long as there were no other systems failures which would significantly affect the operation. It's an accepted practice and that is what would appear to be the case in this instance.
If the aircraft was forced to accept a lower level by Oceanic, (and that does happen quite a lot), that could affect the fuel burn and one would hope that the crew re-planned accordingly. The arrival at MAN with just 5 tonnes does beg the question as to whether this re-plan was effective, or were there other factors involved.
The knowledge that 3t out of the 5t was unusable is very disconcerting. The 747 drinks fuel at a prodigious rate at low level and I would imagine that there was a certain amount of uneasiness on the flight deck.
It would be interesting to know the route the a/c took (presumably northern or polar), and whether diversions to KEF, GLA or similar were considered.
I arrived at LGW a few years back in a 330 with 12t and diverted to MAN due to extreme winds across southern England. It was a direct diversion from 26L to 24 with no delays and I shut down at MAN with 4t. That's on a reasonably economical twin - you can imagine how quick the remaining three 747 donkeys were drinking the fuel in this recent incident.
Are the AAIB involved at all? I suspect not as there were no damage or injuries. Will the occurrence be investigated in-house or on a wider stage? It seems to me that a long accident chain was put in place and only broken at the last moment.
Finally, I personally support any spotter's right to contribute to pprune, and am disappointed by some of the disparaging remarks on this thread - it portrays us (professional) pilots as snooty, aloof, arrogant armholes. Give them a break - they follow aviation closely and would probably give everything to be able to fly as a profession.