Hey Eric,
I am sorry for the delay of this reply,
Hm, I believe you misunderstand the way user come to register on your site, when the user come to your site register, they actually do not need to pay any extra charges, am i right?
If yes, this process is actually not consider as user subscribe on your site.
Unless you have install this 3rd party PayPlan extension from your site, because this extension you can configure to use membership which can integration with Easysocial, in other word, when the user come to register in your site, they need to subscribe first in order to become a member on your site.
http://www.readybytes.net/payplans/documentation/easysocial-registration.html
If you are not referring this, I assume what you mean is when the user become a member from your site, but they feel do not want to continue that user account on your site and they want to deactivate that user account, they can able to do it by himself go to their edit profile page, click on that delete button, you can refer on my attached screenshot below.
But you have to make sure you have enabled that "Account deletion" setting from your profile type.