If the authentication server vanishes then they will have to deal with that, since the customer is right to expect his software to keep working.
A customer will expect to be able to keep moving the software to new hardware, or otherwise reinstall the software and for it to work. This is an issue for companies that sell perpetual licenses to software, and require authentication. I have seen examples of where they have pointed users of older than CS2 to upgrade to that version, rather than trying to deal with older versions. That server failed, and due to the expense of rebuilding it Adobe simply set up a new download with a freely available key. The only Adobe product that I am aware of that no longer has a authentication server operating is Photoshop CS2.
