Transfer ownership of Drive files before deleting a user

To help prevent the accidental deletion of Drive files when deleting a user, admins will now be prompted to optionally transfer ownership of any files owned by the user. Admins can choose to transfer all files the user owns or only shared files they own. If the user is deleted without transferring the user’s Drive files, Google deletes the files the user owned within five days.

For more information:
https://support.google.com/a/answer/33314