there's currently nothing like a fall back yet. But it would be a good feature for the next release!
You have to code it for yourself. Try to retrieve the ID of the featured image with kd_mfi_get_featured_image_id( 'featured-image-2', 'post' ); and if it returns nothing, than output the fall back.
If I have the time I will update the plugin and give it a has_image feature. Perhaps there will be a fall back option too. Like this:
kd_mfi_the_featured_image( 'featured-image-2', 'post', 'full', $fallback );
$fallback could be:
$fallback = '<img src="/path/file.jpg" />';
Look out for a new version next week! ;)