A senior coworker who's been with the company for over 6 years, suddenly approached my desk, handed me their card with info and said, "It has been nice working with you, I told [top boss] that tomorrow will be my last day". It was out of the blue so all I could say was, "Thanks, nice working with you too", as they left.
I rarely interacted with them, but they strike me as an honest, no-nonsense, hard worker. It is unlikely they are getting fired; it is more likely that it is their personal choice to leave.
I guess I can say I am curious about what is causing them to leave. I can venture a few wild guesses, but all of them are just guesses.
My question is this: do I say more than I have already said? For example, do I talk to the coworker more to express any further sentiments or parting thoughts before they depart? Can I ask them about their choice/decision to leave? Can I talk to them to wish them luck in their future endeavors?
What I am trying to deal with for me personally is the question of "why they are leaving", as I don't have a clear answer. And how to deal with that personal to me question is likely the core of "my question" for the Stack Exchange crowd.