Delete related entities on entity deletion?

[petak5]

Should User's Feedbacks to other Users or Projects get deleted with the User or not?
The same goes for Project, should User's Feedback to it get deleted or not?

[petak5]

On meeting we agreed these entities should NOT be deleted.

Rather change the parent entity to none/null or some dull entity and name things like "Deleted user" and "Deleted project" in the UI.