From their FAQ:
You can stop using it and the site will automatically set it as inactive after some time.
It remains unclear what happens to the account – does it get deleted or remain lingering somewhere? It seems to be the last.
URLS:
http://www.demonoid.me
http://www.demonoid.me/faq.php#ui_5
Please note that AccountKiller.com is not associated with the business listed on this page. AccountKiller provides easy-to-understand instructions and guides on how to cancel charges and relationships from the list of businesses on our site, we have no affiliation with these businesses.