To clarify, Google Reader remains a stand-alone product. What is being announced is threefold: 1) Addition of sharing to Google+. 2) A new modern design. 3) Retiring of the dedicated sharing model.
This statement ( It will be impossible to use Google Reader as a standalone product) is incorrect. You can continue reading your feeds in Reader independent of Google+.
So it seems we (non-G+ users) won't be affected.