The expert witness testimony will be entered into the case record. Apple would presumably get access to that record and figure out how it was done and fix the hole. I wouldn’t be surprised if they even had someone in the courtroom taking notes.
You do know that they have already released a newer version of this phone? Presumably this new version is already not susceptible to the method being used by the FBI.
Do you think Apple is going to attempt to R&D a patch for all their earlier 5C Iphones? (Assuming it can even be done.)