Even beeing a mature technology I would´nt say that nothing will ever happen. My old CLP-950 broke after not even 2 years of playing. And at that time it was a mature technology also
. My real upright piano had no issues after almost 10 years.
But I think Yamaha had some issues on this CLP model at that time.
I have a CA63 from Kawai and hopefully soon my CLP 370. I know the CA63 has some issues since a tecnician came to fix some keys. And DP´s are in my opinion not that "perfekt" compared to the action and build of real piano- or grand actions made of wood. I still have issues on my CA 63 which will mostly not be solved.
Mostly the action of DP´s is made of plastic with some felt to absorb the energy of the key pressing down. Then you have some sensors or a sensorbar, perhaps some bearings for the plastic hammeraction.....
Maybe you will even have the wooden keys in some models, but this does not make a difference since all mechanical parts are 99% plastic
In the areas where you have mechanical and moving parts there will allways be wear and perhaps a failure. Here in Germany we have a 2 year warranty on DP´s and 5 years on uprights (at least for Yamaha). I think that quite shows how convinced Yamaha is about how long these things will last on everyday use. I would guess that one out of 10 DP´s will have some issues.
BUT. THis should´nt have influence on your decision. If you want a digital then just go for it. It is more affordable than the real thing and has some other benefits.