The LiveCloud account associated with the premium memberships is a separate account from your users' rotation.infopop.cc account. As a result, if a user changes his/her email address on your site, it will not in any way impact their LiveCloud ID/email address. Users should use whatever original LiveCloud ID/email they used when they signed up for their LiveCloud account.
Note that users can always change their LiveCloud account ID by logging in to account.livecloud.com and updating their email address.
If they can't remember their old email address, then there's not really an automated option to recover the account. There's no other automated way to recover an account aside from your account email address. If this does happen to one of your premium members, however, you can have them put in a support ticket here, and we will be able to assist them in the manual account recovery process. We will be able to look up their LiveCloud account that is associated with their SitePay premium membership account.
Hope that helps!