You'll know when it starts to go. It was pretty obvious in my case when it was time to change it. Progressively worse slip, clutch smell, etc. The OEM clutch is really resilient as long as you don't ride it out hard or doing anything like the notorious 3rd gear start.
I forget who it was but Ed Sims and I were drag racing at Infineon Raceway in 2010 at SAAC 35. We were killing everyone running about 130-135mph 1/4 miles. A third GT showed up and he did a 3rd gear start and unleashed the worlds best burnout of all time and ended his day after that with no clutch. The crowd was in Awe...........