Nitpicks!
The forum won't cease to exist. Its domain name will be dropped from the Domain Name Service (DNS) for lack of payment. The forum itself will continue to be alive and well and in full existence. You'll just have trouble finding it, since DNS is what tells your browser that "internationalskeptics.com" can be found at the address 104.131.54.4.
It's not the URL that's being paid for, it's the domain name. The Universal Resource Locator (URL) is a complete path to a web resource. It includes the protocol (http(s)), the domain name (internationalskeptics.com) and the resource being sought at that domain. For example, the URL for this thread is
http://www.internationalskeptics.com/forums/showthread.php?t=353418
Also, note that simply knowing the IP address that goes with the domain name is not enough. If you send your browser to 104.131.54.4, the webserver will promptly redirect you to the domain name. You can see the change in your browser address bar when it happens. Right now, that works fine, since DNS will tell your browser where to find the domain. But once DNS stops doing that, that redirect will fail. Not only that, but all the URLs provided by the forum software start with "www.internationalskeptics.com". So even if you could get to the front page at 104.131.54.4, as soon as you clicked on a link your browser would give up.
Fortunately, your computer has a system configuration file, usually called "hosts", usually stored in a folder called "etc". In West Coast IT jargon, it's usually pronounced "etsy-hosts". You can put domain names and IP addresses in this file. Your computer will use these name-address pairs instead of DNS results, if present. If Gord adds "internationalskeptics.com 104.131.54.4" and "www.internationalskeptics.com 104.131.54.4" to his hosts file, he will indeed be able to browse the forum while the DNS record is unavailable. (This, by the way, is more than sufficient to prove that the forum has not ceased to exist.)