This is the piece on the BBC News website that spurred me to rebook, expecting money back:
You can apply for a refund. Even if it is only the outbound portion of the flight that is cancelled, you can still get a refund for the return leg, assuming you do not want to use it.
Or you can chose an alternative flight - perhaps on an earlier or later date. In most cases Ryanair will offer you another flight with them.
However, the Civil Aviation Authority (CAA) says that if Ryanair fails to offer a place on an alternative Ryanair flight within a reasonable timeframe then you have the right to be booked onto a different airline at no extra cost.
http://www.bbc.co.uk/news/business-41305537
Surely, this applies to me, since Ryanair has cancelled both the Stansted Flight to Derry and the Gatwick flight to Belfast?