The only thing to worry about is if you use the existing process where you buy a book from the Amazon store, download it locally to your computer, then copy the Amazon DRM'd ebook from your computer to your Kindle by USB. The step to download the book from the Kindle store to your computer will be going away, Kindle books from the Kindle store will have to be directly delivered to Kindle devices through either WiFi or cellular.

Being able to generally copy books to your Kindle by USB will not be going away. Books on your Kindle will not be going away, other than the historical reasons why Amazon pulls ebooks from people's devices (but that's not changing at all here). If you have a collection of DRM-free ebooks you can continue to use those and side load those by USB.