Henry
I'm just not sure what was 'obvious' on that flight, we're all busy trying to overlay our collective knowledge of systems, operations, and aviation good practice (airmanship) on to what is a very perplexing event. I do agree that if there was sufficient doubt about the accuracy of the fuel contents at Dalkieth the 'obvious' thing to do would be RTB and call the engineers from the comfort of the office. That makes me think there was nothing displayed that was obviously abnormal to the crew until it was too late.
There is some fact amongst all of this, the 4 switched fuel pumps were not in the correct operating positions for 'normal' flight (IF the final fuel contents were displayed accurately in the cockpit). The aircraft had been airborne for a period of time about equal to it's legal fuel endurance, so displays and warnings aside it should have been on the ground or in the final stages of legal flight at the time of the impact (and to be fair it was only 1.5 miles from base so might well have been on the ground with legal indications of MLA as far as the crew were concerned). With each unit having a specific standard fuel load, in this case 400kg, you don't need to do too many shifts to know how long you can remain airborne and when it's becoming a little tight but still legal.
My opinion is that the handling of the aircraft in those final minutes will remain a mystery, there just isn't the evidence to sort out a logical chain of events (perhaps this accident will force some form of data/voice recording for the future). Radar trace, lack of emergency calls, eyewitness descriptions just don't paint the full picture to enable even the most experienced on here to say with certaincy how it unfolded.
I still think the crucial evidence of how things got to those tragic last few minutes is yet to be tested, ie...what were the displays indicating? were there any known faults in the tech log, had the aircraft recently had faults and rectification, did the pilot shift handover highlight any non urgent 'snags'?. For instance it's quite legal to dispatch with many parts of the aircraft in an unserviceable state, such as one transfer pump, one landing light, one screen out (Literally on one occasion while it was away for repair..... very odd scanning a large area of black masking tape out of habit!). That said, the report indicates the aircraft was fully serviceable at dispatch.
I think there will come a time on this thread that we will all have to accept that we just don't know, due to the lack of recording of data and voice.