How to hide webform block after submission for anonymous users?
When a visitor submit a form, cookie with a name "webform-123" (123 - webform ID) save in his browser. In the block visibility settings use the cookie existence check with PHP:

&lt;?php 
$match = FALSE;
if(!isset($_COOKIE['webform-123'])) {
$match = TRUE; 
}
return $match;
?&gt;


If the cookie does not exist, the condition will return the TRUE and the block will be displayed.