Similar case, other company. I booked a car via Hertz in Miami, as it is the road tolls are collected much later once Hertz receives the plate pass charge, but by then my credit card had been cancelled due to fraudulent activities on it, so Hertz could not charge me. I had all forgotten about that, until next time I rented from Hertz in Miami some months later, I was only reminded when I wondered how I could have raked up that many tolls in that short a trip, and then it dawned on me why.

OP, if you have an account and made the booking associated with that account, Ryanair is unlikely to forget. But not like they are going to hound you for it, they'll just charge you when you get the chance.