Midnight Cruiser,
The Quote in your post reflects the view of the CAA (rather than BA), which was asked to approve the extension for another 6 months. Some of the criteria for an extension to operate foreign registered aircraft is that the UK company (which is BA in this case) has to demontrate that the nature of the extension is temporary and that they intend to transfer the fulfilment of the existing contracts to UK registered aircraft as soon as possible.
BA needs another Freighter, but for some reason (probably commercial) they just did not want to follow up on that promise and chose to play the system as long as possible.
Chances are very little that BA would pull out of freight. Freight has much higher profit margins -more than passenger ops- and is projected to do so for the forseeable future.
If anything, BA will expand the Cargo business. After all, most of the other profitable major Airlines in the EU operate Freighters (Lufthansa, KLM, Air France....). Therefore it is more likely -but not anytime soon- that BA World Cargo will bring the Freighters inhouse.
What happens then to the GSS employees is pure speculation. History and the small nature of GSS provide a clue, that BA would bring the crews along, probably with a B-payscale and at the bottom of the seniority list, while preserving their current position on the freighter fleet. Any switch to a passenger fleet then would have to happen based on their new BA seniority.
In the worst case scenario that could mean, that if a B744 freighter captain wants to switch to the passenger fleet, he/she could do that as F/O on Airbus 320 or B737. (Or something like that.)