I have always wondered what would happen if the IP of your NS was to change but you had the IP forward and backward resolve right after. I.E.

We use NS1.NETHOSTERS.COM

Now if that got changed to a different IP what would happen? We have hundreds of domains on that NS that use that NS, how would we go about changing the IP without editing every single domain or is that possible? I am just wondering in case the place we have our servers setup ever says "We are not providing any more services" What we would do. (We already have another server in another location under a huge provider just in case (ns2.nethosters.com) but still I like to be cautious.

Fortunately you would not need to change every IP address, simply the primary IP address for your name server. You can do this through your registrar and all of your domains will be updated automatically.

The way most providers handle this is to change the IP Address of NS1, while waiting for that to propagate, cahcing servers will have to rely on the secondary name server (this is where you sweat bullets hoping it does not fail :D). After the primary has switched over, you then switch the secondary to your new netblock and again sweat bullets hoping your primary does not fail while the secondary switches.