The answer is NO, a third a/c has not left the fleet.
Planned visit to enable the engines from G-OZBB to be swapped with those on G-MPCD.
All Airbus aircraft have a Flying hours & Cycle limit, which can be increased, it has been already twice on the A300-600 by Airbus.
There has been an increase with the A320FAM as well.
Boeing are also coming up with figures for all the Boeing/MD fleets to meet FAA requirements.