It's possible that Ryanair has marked the flight as cancelled and you just didn't receive the email. Do you see the cancellation notice when logging into your PNR on Ryanair's website? If you do, you can already change/refund the flight. If you don't, you have to wait until Ryanair marks your flight as cancelled before you can do anything. (The e-mail should arrive within a few hours of Ryanair marking the flight as cancelled).