Deleting tokens

What happens to a token which has expired - is it necessary to explicitly delete it, or will it be automatically removed.

Is it an error to delete a token which is no longer present? If so what is the error that should be expected? Are there any other "expected" errors (e.g. would it potentially be an error to remove a token which is currently "in use" - e.g. is required to prove the client has the authority to establish a link which is currently established)?