I have a Shure V15VxMR cartridge with about 400 hours use at low tracking force (1.5 grams) on primarily new audiophile records (150-200 grammers)using a high quality turntable. I realize you can look under a microscope and see if the stylus is chipped, but what is the general criteria when considering a replacement stylus. I know in the old days it was either 500 or 1,000 hours of play--I cannot remember the exact figure.
Based on your criteria, 800 hours of playing time is a reasonable estimate of the stylus life.
Typically, the diamond stylus does not chip. It wears down and flat spots replace the original stylus shape. Replacing the stylus returns the cartridge to like-new condition.