Manage users
Deletion
At the moment, there is no real possibility to delete users, because project data that is linked to the users becomes invalid.
However, depending on project scope and purpose, it should be possible to remove users completely while retaining a consistent state for entities.
Other stuff
Similar problems arise when removing users from projects. It must be possible to manage users so that mentioned use cases (and other related use cases) are possible.
Estimation
5 Story Points