You still have the ability to review any product that says discontinued. Also, for some reason, upcoming items are also listed as discontinued as well. Silly little glitch, but it shouldn't affect you. Let me know if you can't review.
You will not be able to search it normally. You can check my retired wishlist if it was a popular product, search the words of the product at the top in search bar and then choose reviews, or just search around similar product and look on the left hand side for a review of it. Message me if you need help.