Note that a composite wing will react differently than a metal wing at ultimate load. So Boeing can not do what Airbus did with he A380. Recall that the A380 experienced a failure. The metal went beyond yield and broke.
With the 777x wing, there is really no yield point and until you hear fiber break and delaminate, you can bring those wing up the same load path again.
At least if the failure is in the fuselage, they can take the same approach as the A380 and beef up the door structure to continue the test and fix it later. The most important thing is making sure the wing is good to Ultimate.
You can't use a failed specimen a second time ( fixed up or not) . independent of the material composition.
The A380 wing test failed just below design targets. i.e. the simulation model was "good enough" but had a directed error.
Certification requirements were met adjusting the simulation to get rid of that directed error
and then adding material in the right places and rerun the simulation. success? -> method accepted and certification granted.
This could not have worked for the 787 wing test where damage started to develop
long before any sufficient force to create predicted damage was applied.
Additionally defects shew up in "unpredicted" places.
The simulation was fully unfit for the task.