I replaced my sprockets out of habit, I always put fresh sprockets on with a fresh chain. My rear sprocket showed no visible wear at all and the front very slight wear with no lube at about 23,000 miles and the chain was just stretched some. I probably could have gone another 10,000 or so but opted to change the set as a set.

I learned all I need to know about life by killing smart people and eating their brains.
Eat right ,Exercise ,Stay fit, Die Anyway!