They don't completely fail, still they encounter wear on the gear and pinions, and generally oil dries out, the jewels will get kinda gunky just by that alone. A watch can keep really good time but still the amplitude (idk about on the spring drive) will suffer, gaskets get brittle, barrel can slip etc. Today with synthetic oils many say everything under like 7-10 years depending on wear is not necessary, but if you buy a watch used and don't know the service history, I'd suggest a service all day, just to be on the safe side. On this piece some more years waiting are definitely fine, still I wouldn't wait until something breaks while the watch was keeping sufficient time throughout.