They will eventually wear out, but they should last for many flights if you take care of them. It would be best to inspect the props and tops of the motors for wear prior to each flight. Replace either if you notice any damage.
I'm sure DJI will start selling a replacement prop kit for the tops of the motors. They offer a kit like that for the Inspire 1 now for $5. It'll be much easier and cheaper than trying to replace the entire motor