Mentioned before, the man from Barnwood (1989) asked the question at the MOD Navigation Training sub-committee, "what is the long term future of the navigator branch,?"
It was becoming obvious 25 years ago that fewer would be needed. The nub therefore was 'when'. What is now apparent, and was really apparent when training stopped, is that they stopped too soon.
With a GR4 OSD. of 2025 a new nav could have expected a full flying career to the 38/16 option point. Older navs could serve to 55 so job done and training could stop.
Of course that ignored the fact that navs could PVR too.