From a contractual standpoint, where is the physical boundary between Boeing's sphere of responsibility and that of Rolls Royce, the engine supplier? Would it be in the area where the engine nacelle attaches to the wing pylon?
Presumably, the contract under which RR supplies its engines to Boeing would include detailed specifications regarding the nature of the fuel composition/condition to be delivered by the 777's fuel system at the Boeing/RR interface. It seems unlikely that the contract would have specified the sort of volume of water/ice which arrived at the FOHE. If so, RR could argue that the fuel delivered to its engine was outside specification and, therefore, they (and their insurers) are not liable for the loss of the aircraft.