Pinkman,
I think that you have got a little mixed up. As I see it there are 2 issues.
1 Why was there a double engine "failure" in so far as the engines failed to respond to inputs from the thrust lever or autothrottle. This has become such an involved investigation that the AAIB with the help of both RR and Boeing have yet to come up with an answer. It is interesting to note that there have been no AD published that would provide a clue as to where the investigation is going and why.
2 What were the crew reactions during the 50 secs or so that they had after becoming aware of the situation that was presented to them where there was no checklist for or they had previous experience of.
If as reported the Captain raised the flaps to the G/A position so reducing drag I would suggest that the 2 crew on board did everything that they could to retrieve the situation other than get out and push it. The fact that they all walked away from it is down to their actions and a big dose of luck.