Just test this plugin and then indeed once js is off, the capatha will disappear. As *Ricardo* points out, Google’s demo works fine with js off.
Here is a walkaround for this issue:
In the plugin folder, find a file called base-class.php, and then search for “display_captcha”. At the end of this method, just add the following code:
echo '<noscript><div style="width: 302px; height: 352px;"><div style="width: 302px; height: 352px; position: relative;">'.
'<div style="width: 302px; height: 352px; position: absolute;">'.
'<iframe src="https://www.google.com/recaptcha/api/fallback?k=YOUR_SITEKEY" frameborder="0" scrolling="no" style="width: 302px; height:352px; border-style: none;">'.
'</iframe></div><div style="width: 250px; height: 80px; position: absolute; border-style: none; bottom: 21px; left: 25px; margin: 0px; padding: 0px; right: 25px;">'.
'<textarea id="g-recaptcha-response" name="g-recaptcha-response" class="g-recaptcha-response" style="width: 250px; height: 80px; border: 1px solid #c1c1c1; margin: 0px; padding: 0px; resize: none;" value="">'.
'</textarea></div></div></div></noscript>';
Don’t forget to replace YOUR_SITEKEY with your sitekey.
Hope this helps.