To cheer you up I thought I would let you know that it's not only NAT's management with the wrong attitude towards leavers.
When I decided to retire after 24 1/2 years service I sent an email to my section supervisor, room manager, her deputy as well as the head of department and his deputy.
My section supervisor and my head of department were top of the class. The latter was old school and came to see me and have a chat within a week of my email to make sure I was making the right choice etc. His deputy said he would visit on last day minus one, and didn't. My room manager was on leave but did send me an email but her deputy didn't even reply to my email and ignored me on the few times before I left when my shifts happen to be the same as her 9-5 mon-fri.
Only my shift supervisor came to my leaving do and two years later I've not bee replaced either (HM Goverment cost cutting).