Deletion of your account will block any live or admin access to your website. It also automatically stops any paid subscriptions related to this account.
To delete your account, you can click on the Cogwheel Icon in the top-right corner of the admin panel > expand the Settings tab > General then scroll down to the Delete Site button and click on it. After you have answered the short exit survey, you will have to confirm that you're the real account owner by entering your admin password.
If you would like to transfer your custom domain before your account deletion, you can refer to this article.