The person leaving deserves a farewell that recognizes more than the inconvenience of their absence.

Departures tend to get discussed logistically. Who will cover the work, who takes the keys, how the gap gets filled, all of it framed around the hole rather than the person who is going. Someone can spend years somewhere and leave hearing mainly about the trouble their leaving causes. That is a thin ending for a long stretch of contribution.

Say one specific thing about what a departing person did and what it meant to you, separate from any handover. Say it directly to them rather than in a group message.