Two ways to look at this, I think.
There is a history, for whatever reason, for SOME NC rear wheel bearings to need replacing at typically around 25k miles. Now, we can put forward theories for this, it's still unclear why they have failed at this premature mileage. They ought to be good for, well, a lot more than that, 100k miles maybe?
The 2 views? As Dave says, if it ain't broke don't fix it. On the other hand, if you have the ability to change them and your bike is at that sort of mileage, do you want to wait and see what happens and find they start to go when you a