The Stradale ceramic discs are SUPPOSED to last for the 'life of the car' but whether that is true or not, I don't know. I believe that the only way you can check their wear levels is by removing them and weighing them, it cannot be checked by the usual visual inspection. They have a minimum weight stamped on the discs, under which they should be changed. In fact on some Ferraris, when they go below this weight, a sensor is triggered and the car goes into limp mode! They can also suffer from stone chipping which would mean they need to be changed.
Once you are used to them, they are fantastic but you are right, they're very costly to replace