Sometimes there is just nothing to say not everything is nefarious it could also mean that even if you think you had a close relationship to your colleague it really wasn't so close at all because otherwise they would give you a heads-up afterwards.
Is it reasonable to say "X is no longer with us, we'll figure out their responsibilities with hiring a replacement, dividing areas of ownership, etc" shortly after they depart (for any reason)? Or should the team have to put two and two together after realizing they aren't coming back? I feel like the latter is too common.
