As usual for these types of questions, the answer has got to be "that depends". The way you handle the clutch, the fluid you use in the primary, how often you change the fluid, how well you keep the clutch adjusted, etc.
But all the caveats out of the way, you should have plenty of miles left on your friction plates. If you have to open up the primary for some reason, just look at the thickness of the friction plates. I suspect you will see they have plenty left. Just to be safe, however, check this out: