I'm almost sure the cost for the planned repair are several times as high as the restvalue of this 16 yr old 777.
In a write off scenario, we would have to take out al re-useable, valuable parts of the BA 777, such as the remaining engine, landing gear, APU, cockpit and Avionics bay LRU's, controls,flaps, actuators maybe interior and see what value is left in the badly damaged airframe.
E.g Delta bought a reasonable complete 10 yr old 777 for $8 million recently.
I guess this repair including all dramatic structure replacements, testing and recertification is going to costs easily over $25 million, maybe 50. In a few years A350 start streaming in with BA and this then off standard, heavier 777 is probably the first to go.
It seems economics is not the top priority in this project, other things are just more important.