An empty chair can organize a gathering more strongly than the people sitting down.

The person who is not there can shape a gathering more than anyone present. The one who died, the one who was not invited, the one who fell out with everybody. Conversation routes around the absence, the seating acknowledges it, and everyone is aware of it while nobody names it.

It often helps to say the name out loud. A brief, simple acknowledgement releases the pressure of everyone pretending not to notice. The absence is going to be present anyway, and letting it be spoken usually makes the rest of the day easier rather than harder.