Clearly Hertz believe FR breached contracts by allowing GDS bookings which could have major impact if holiday companies book flights instead of people doing it. Hertz must be quiet confident they will win any case as they know FR wouldn't just leave it.
Point is that FR have been using GDS for over a year, hence could understand if it was on day 1 but a year plus is not even close.
Problem for Hertz will be that it will lose a substantial portion of business who booked via Ryanair, now they will book everybody, Hertz will of course pick up some of this business anyway maybe at a better price.
However I doubt that this will compensate as simply their fleet buying decisions will already have been made and losing a substantial element of business will be a struggle.
Will be interesting for some of the Hertz Franchise holders who probably will have a claim against Franchise owner. If they acted to damage their business by cancelling a contract with a major business provider.