Thank you! Here's how I ended up solving the issue
1. I set up a new Joomla user group for members, called "GSFABA Members," with Registered as the parent group.
2. In Paid Subscriptions > Plans > [my plan] > Access > Subscribers User Access Level Settings, I set the User Group to GSFABA Members.
3. In Community Builder > List Management, I created a list called "All GSFABA Members." In the Usergroups field, I chose GSFABA Members.
4. I created a Community Builder Userlist menu item to display the "All GSFABA Members" list.
When a subscription expires, the user gets downgraded to Registered, so they're no longer in the GSFABA Members user group, and their profile is no longer displayed in the user list.
I hope this helps someone else!