Get a grip!
Your WO 'mate' was recognised through promotion.
He leaves with skills he did not have when he joined.
I daresay he leaves with many happy memories and many good friends.
He leaves with a gratuity.
He leaves with an index linked pension.
If he really is that upset because no Officer(s) came to his farewell bash then he has been promoted (way) above his ability.
I would never have dreamt of turning up, uninvited, for a farewell bash as I would probably have been shown the door.
Had I been invited, personal or 'open' I would always go along.
In my experience of WOs (the good ones that is).
they do not need to be patronised by some Officer, senior or otherwise.