Expire Draft Posts Only

Sure!

You will have to change this part:

if($cat_id > 0)
					{
						// Do only the last 50 (by date, for 1 cat)
						$myposts = get_posts('category=' . $cat_id.'&post_type='.$the_type.'&numberposts=50&order=ASC&orderby=post_date');
					}
					else
					{
						// Do only the last 50 (by date, ALL)
						$myposts = get_posts('post_type='.$the_type.'&numberposts=50&order=ASC&orderby=post_date');
					}

the get_posts() will retrieve published posts by default, feel free to alter this to draft, more info at
http://codex.wordpress.org/Template_Tags/get_posts#Usage