Some of GB's routes are operated using BA route licences that go back to BEA times. I don't see BA giving those up for one moment. GB clearly thinks it can go it alone with it's remaining route portfolio and the core holiday company business.
Route licenses are irrelevant now for any routes within the EU.....which is the main part of the GB network. Any EU airline can operate the routes.....therefore even though the "BA" code would be lost, GB can happily keep on operating.
However, slots are a different thing.....do GB operate everything on their own slots or do they utilise any BA slots?