I'd have thought there were two main options:
1. Repair what they can in-situ, then add enough strengthening inside and outside to make it airworthy (but ugly). Fly it empty and depressurised to Boeing or somewhere that can do the job properly in a controlled environment. This will probably involve the replacement of a large section of the fuselage with a new construct.
2. Attempt to get it back to 'showroom standard' while it's parked outside at LHR during the winter (if they can't hire some hangar space). Largely a voyage into the unknown, I'd guess.