The just released July 22 issue of Aviation Week & SP has extensive article on the fire. I can't retype the whole article (online version is for separate subscription) but I can quote some parts (page 23):
....Insiders also quietly note that the composite structure held up well to the fire. Compared to conventional aluminium, for which FAA tests have shown burn-through times of 30-60 sec in intense fires, Boeing flame tests exhibited longer burn-through times for sections representative of 787's composite laminate skin. The aircraft maker also points out that although the fire was severe enough to visibly char the exterior of the skin, the fire did not penetrate the surface.
The composite repair technique, although expected to be complex and costly, is also likely to be relatively easier that a similarly scaled repair to an aluminium-skinned airframe because no testing or checking will be required to match the ductility of the replaced skin with the surrounding structure. All aluminium aircraft skins are subjected to annealing, a heat treatment which makes them more workable and reduces internal stresses, and skins adjacent to those which have been affected by fire must be checked to evaluate their condition.....