Thanks Kyle,
Yes, I have only one pad subscription which allows full access to the Kunena, so I'm thinking no need for any sort of other intervention.
I just wanted to make sure that once the account is expired by CBSubs that it stops the Kunena emailing users who had followed/subscribed to posts or categories.
Once they renew their membership and reactivate their account the Kunena notification functionality will resume for that user as normal.
Does this sound about right?