There a two options there, with different outcomes.
Deactivating/disabling a team member
If someone is leaving temporarily the team, that's the way to go.
Deleting a team member
Use this option if you want to delete the team member, because s•he left the company. The data history (moods and comments) is kept within the team.
WARNING: we cannot undo the deletion, so please make sure you know what you do.