Why is it that if you give people licences you think they will all leave? Have you thought that people join up because they want to be in the RAF. Sure it'll be handy once they leave, but I expect the majority will stay in (there's always the exception).
In order for the aircraft to be operated in the civil role it must be maintained under EASA regulations. FSTA engineers will operate under Part 66 regs as will the RAF engineers .