Region not displaying in module
The code to print page regions must be in your theme's page.tpl.php file, not in a file in a custom module.

If you want to put your code in a separate file (sidebar.php) you need to make sure it's included in page.tpl.php, like

include './sidebar.php'; // file is in the same folder as page.tpl.php


or

module_load_include('php', 'MYMODULE', 'sidebar'); // file is in a module folder


hope it helps