Checking whether all the related entities get deleted if we delete a user should be a part of Unit Test for models which will aim to check the database relationships.
But still we can have an API test which will Assert that we receive the user data along with the User details and data gets deleted when we delete the user.
But it will be in next version for this API when we have a more advanced serializer.
So let us focus on only auth user for this version.
What do you think @bobsilverberg  ?