All users can be deactivated and then archived in the Administration > Users module.
In this status, these users will no longer be selectable in the various user lists (Projects, Activities, Authorisations, etc.).
In other words, it is only possible to delete a Collaborator from the environment if he or she has never been "managed" in the Abraxio sense, i.e. for whom timesheets or assignments have never been activated in the Management tab.