add_action('wpf_tags_modified', 'my_wpf_delete_user', 10, 2);

function my_wpf_delete_user($user_id, $user_tags) {

    $contact_id = get_user_meta( $user_id, 'infusionsoft_contact_id', true );

    if( empty( $contact_id ) || ! wp_fusion()->user->has_tag('GFTB Full Membership - Activated', $user_id) && !user_can($user_id, 'manage_options')) {
        wp_delete_user( $user_id );
    }

}