One way to prevent files, uploaded through Caldera Forms file fields, not set to be added to media library, from being deleted.

dont-delete-private-files.php

<?php
/** Wait until caldera_forms_core_init hook so we know all actions were added **/ 
add_action( 'caldera_forms_core_init', function() {
    //File delete is attempted first here, but if an email should send, the file isn't deleted//
    remove_action( 'caldera_forms_submit_complete', array( 'Caldera_Forms_Files', 'cleanup' ) );
    
    //If email is set to be used, we wait until email is sent to delete on these hooks:
    remove_action( 'caldera_forms_mailer_complete', array( 'Caldera_Forms_Files', 'delete_after_mail' ), 10, 3 );
    remove_action( 'caldera_forms_mailer_failed', array( 'Caldera_Forms_Files', 'delete_after_mail' ), 10, 3 );
    
    //Just in case of a never completed submission or some other issue, a CRON job is used to delete the file
    remove_all_actions( Caldera_Forms_Files::CRON_ACTION );
    
}