No, the Veracross system does not automatically remove members/users from portals. As a part of the Start School Year procedure that is run annually, Future Parents become Parents and are automatically added to the Parent Portal in the following overnight scripts, but are not get automatically removed from the Future Parent/Family Portal.
Portal membership should be maintained by either running the Disable or Remove Members with Strategy Mismatch procedure from the action menu of the Portal Admin detail screen. For more information on Portal Membership Management, please see this documentation.
NOTE: This information is only relevant for Schools who have a Future Parent or Future Family Portal, where these future Parents already have Veracross user accounts. For information on creating new user accounts for parents, please see this documentation.