No. The IP addresses listed for your site in your member control panel may change as part of how our load-balancing system works (although that doesn't happen often) or if a site using a particular IP address suffers certain types of attacks. If this is of concern to you because you are configuring third-party DNS, please see this FAQ entry for instructions.
If you or someone else has cached or is otherwise using an IP address that is no longer listed (perhaps due to not following the instructions above), it is generally not a problem. At any time, any of our dozens of member site IP addresses will provide your site, whether they are listed or not. We will announce if we ever permanently remove any IP addresses from this pool.