A now retired member of the Concorde flight crew told me that the engine problems were down to one engine (can't recall which one) ingesting runway lighting debris and the adjacent engine ingesting neat fuel which was interpreted as a second failure on the flight deck. The ingress of fuel into the engine was a transient condition and full power would have been available after it had sorted itself out. Once both engines had been rolled back, Concorde was then on the back of the drag curve. Had power been maintained and the ruptured tank had fully drained, there may have been a better chance of a survivable outcome but it's a purely academic discussion.
The flame front could not advance faster than the airflow so it begs the question what ignited the fuel ? It was thought that damage in the wheel well caused electrical arcing which by some means of a disrupted airflow in that area, ignited the fuel. The reheats are thought not to have been the source due to the airflow speed being greater than the speed of flame front advancement.
Either way, it was a very dark day in aviation and has revealed once again the consequences of lax attitudes to process.