From this link:
there is a link to the list of books in your library you can "rescue"; I rescued all mine, simply confirming Title, Author and an official link (Author's website or Publisher's website). In this way, from what I understood, all the reviewes I posted for those books are safe. I suggest you to do the same, then, if later one you want to complete the details, you are always in time.
As I said I don't know what is happening, before Goodreads I used LibraryThing, and still am, and LibraryThing is still using Amazon search engine to retrieve the books details and covers. My major effort is in maintaining that library up to date, Goodreads is more or less a back-up, so for me is not an issue if they don't link Amazon, at worst I will not record some books. But if you use Goodreads as your main library, than this could be a problem for you.