Back in the good old days of bonding many of us left airlines without paying them back.
All of those contractual bonds that I am aware having been pursued in courts ended in nothing and nobody ever paid anything.
If you want to talk legal then the first thing to determine is which court is responsible for the case and you might be surprised to find out that very often it is not the court stated in the contract but the court where the facts actually took place.
In the case of a company like ryanair it would most probably be a court of the country where you were based before resigning as stated in the 2007 Lugano Convention.
Then of course the law of that state applies regardless of what it is stated in your contract as defined by another EU treaty like the Convention of Rome.
At this point I seriously doubt ryanair will risk a curt case they will loose, especially because the law system of any country but Ireland would slap them hard.