On way out of a job, what would you want people to say about you?
(This is not about me.)
There is still a slow cascade of single-company lifers leaving. That itself is such a crazy concept, one company, so many years—although I guess in aerospace each major project is bigger than many companies, so it's only crazy of you read the label without looking in the box. But that's not the point.
Some people leave, and you just think, "ok, bye". It doesn't matter much—a semi-horrible thing to say, but no one can be significant to everyone. Some people leave and there's an emotional gap for a while, and it's difficult to cover their work, but it all smooths over after some time.
Some people leave and you think, "uh oh, we are screwed".
Again, everything smooth over after some time, but that time is not fun or interesting or desirable, it's just a terrible slog to recreate poorly what someone else was doing with one hand and half attention. There is an obvious gap without an obvious solution. It's like a monument inverted—a person memorialized in absence.
You want the thanks and congrats and good lucks and so on as you leave, but a few uh-ohs are an unintentional compliment you could raise your glass to.