Accounts cannot be deleted so we cannot be impersonated by anyone registering and using the same username in the future. Also note that Automattic Inc. owns wordpress.COM and also many other products and services listed here https://automattic.com/ that require a wordpress.COM account. Therefore, account deactivation is provided and account deletion is not provided.
Registering an account here required
(1) your consent to the Terms of Service http://wordpress.com/tos/ and all policies made under it found in the support docs like this one for Deleting Accounts http://en.support.wordpress.com/deleting-accounts/,
and
(2) an email address.
Any personal information you posted anywhere was posted voluntarily. Both the email address and personal information can be removed or replaced at any time.
You may want to read this support doc:
Private User Data https://en.support.wordpress.com/private-user-data/ and other information disclosed in the privacy policy https://automattic.com/privacy/
Here's how to deactivate your account:
Although username accounts are not deleted, so you cannot be impersonated and have your reputation affected by anyone registering the same username in the future, there are steps you can take that amount to removing all personal information and result in leaving only a throwaway email address behind. http://en.support.wordpress.com/deleting-accounts/
1. You can go to My Account->Edit Profile and remove all data except the account name and an email address. Create a throwaway email address and change the account email to that throwaway address. This only leaves the username behind.
2. To unsubscribe from email sent to you from WordPress.com, go here and click on “Block all subscription emails from WordPress.com”:
https://wordpress.com/settings/notifications/
3. To ensure the account is locked up tightly, visit this site, generate a password of 15-20 characters, and change the account password to it:
http://www.thebitmill.com/tools/password.html
4. To hide your Gravatar profile, login and on the bottom right hand corner of your Gravatar profile page you will find a "hide" button visible only to you that you can click. http://en.gravatar.com/support/profile-privacy
IMPORTANT NOTE: Deleting blogs and/or blog content or making the site private does not remove indexed content from the SERPs (search engine page results) and we cannot help with that. Google and Bing only clear their caches of deleted indexed content that produces a 404 (page not found) every 3 - 6 months. To completely remove an entire page from Google search results after it produces a 404 (page not found):
https://support.google.com/webmasters/answer/6332384?hl=en&ref_topic=1724262&vid=0-635749429504660340-12158368555624983465&rd=1