KLM still fly into Humberside every day without controlled airspace, and did so at Norwich for many years until very recently. However at EGNV I understand they stopped routing via FAMBO some time ago because of the number of encounters with military traffic, and now always route to/from the south west inside controlled airspace. I don't believe a withdrawal of the Durham CAS would cause KLM to leave. Then again I don't believe the CAA will withdraw CAS around EGNV unless someone in the aviation community argues for it - and who would?
NS