I have seen the same thing as hungryboson. New books show up in the Kindle PC app, looking no different than they ever did. It appears Amazon was only interested in stopping transfer via USB cable.
Presumably, I would lose access to the content if I closed my Amazon account--but for some reason, I always thought that was the case. It probably shouldn't have been, but I know the apps and devices check back in with your account, particularly after an update.
Similarly, I always thought that my heirs wouldn't be able to inherit my kindle content. In fact, there was quite a bit of discussion on that point years ago, long before Amazon made the current change. Whether we call the books purchased or licensed, they were always tied to a particular account, at least when used on Amazon devices.
The same is probably true to an extent of some other vendors. When Barnes and Noble end Nook service in the UK, someone else bought it and honored the book purchases but didn't support other Nook content (like games), so people who had bought any non-book content were just out of luck.
For that reason, it's probably always better to buy physical books, but I just don't have the room anymore. And ebooks are easier to use for research purposes, anyway.