Hi cordwainer.
It is very possible the explosion emanated from the tail section. I had thought that all the missing skin had burned away. An explosion is a better surmise.
I think the wing box and both nacelles are inverted, but you have me wondering. The flat, squarish section centered between motor mounts seems to be the ceiling of the hold, but I wonder if that is the floor of the cabin. Either way, it is part of the “wing box”, the strongest structure in the aircraft.
In any case, I think there is structure connecting tail to wing. If the wing spar held the wing together engine to engine, (#2-#3) it is more than reasonable to expect the keel beams kept the tail with the wing.