The crystals do not exactly wear out but the clock is conditioned and calibrated at the factory. Over time the calibration will drift and eventually the unit may need to be returned to the factory for recalibration. I cannot advise when this may be . The top of the range Vivaldi clock actually generates a warning display when it becomes necessary although this feature is not available with the Rossini clock.
I have been using dCS wordclocks ( three of them) since the early years of this century and have not yet had to return one to the factory for this purpose. NB: As the clocks take time to reach thermal stability from switch on mine have been/are left powered all of the time ( either full on or sleep mode).
So I think you can be fairly confident everything else being equal as at worst it won’t be broken, it just needs recalibration.