From the forums in CJU (posted 03-01-01) :
There has been some discussion concerning a relatively new feature that allows merchants to expire links. I want to explain exactly what this means and why a merchant would want to expire a link.
When a link is set to expire, it takes 30 days for that link to expire. A notification is sent to all affiliates who are using the link that they should remove the old link and replace it with another link. After the link expires, it is no longer available to affiliates in the "Get Links" section. The expired link will continue to serve and track after it has expired.
It is not a good idea to keep using an expired link because the merchant is no longer supporting it. Although the link will continue to serve and track, the merchant may no longer support the destination URL page.
Most merchants expire links because they either have too many of a particular type of link or a link was not performing well and they want affiliates to find better their performing link.
Sometimes when a new feature is released, it is used by many of your merchant partners all at once. This can cause affiliates to think that things are changing for the worse or that merchants are acting rashly.
We know it is a pain to switch out links but in the long run, everyone will benefit from using the most effective links. The good news is you have 30 days to switch out expired links.
I hope this helps.