The non-NATS world will always need ATCOs, particularly as NATS trains less ADC/APP people thus reducing the supply somewhat. Admittedly last year Filton closed and seven jobs (or thereabouts) were filled as those guys moved elsewhere but that was a one off. I'd go for it if I was you, you'll find a job, you just may have to be prepared to move but as a mil ATCO that won't be too much of a change presumably.
If you are thinking of Resource at Cwmbran for the civvy courses, have a chat with them as to your chances and if they know where the most likely places are needing staff in the next couple of years.
Good luck with it.