There is no 7th generation iPod (yet?). The current generation is the 5th, which is also the only one capable of running iOS 7 and later, where iTunes Radio was introduced. I assume this is what you mean. I also assume the "Radio" icon/tab at the bottom of the Music app on the iPod touch is what you are talking about.
In this case, there is no way to turn it off. When you've noticed that it's gone, it's because you were not connected to Wi-Fi, and the Music app detects that and doesn't show you the button because you can't use it without an Internet connection. So, I guess one way to get rid of it would be to just disable Wi-Fi, but then you're stuck without Internet access if you use any other features on the device that require it.
Basically, there is no option to permanently turn it off. However, you may be able to move it so it's harder to click on. Click the "More" (three dots) icon at the bottom of the Music app, then click the "Edit" button/link in the top right. I'd drag Radio all the way to the right, then drag something new down from the top to push Radio all the way off the side. Click "Done" to save your changes.