Like already said, pressure plates and inner hubs typically don't break unless mishandled during disassembly or assembly. The factory basket tends to wear out first. Can't really give you a timeline as to when it will wear out. It depends on how you ride and how hard your are on the clutch. If you race, gate drops are brutal on the basket. Even my billet Hinson basket is starting to get grooves. Again, the fibers and plates will last different amounts of time depending on how you ride, what they are made of, and the quality of the service your provide to maintenance.
There are things that you can do to prolong the life of your clutch.
1. Get the 89 clutch update kit (if you don't already have it)
2. Increase the clamping force applied to the plates for less slippage.
(A) Several ways to do that:
1. Get heavy duty springs. ESR and many others sell these
2. Use Cleigh's heavy duty clutch mod (Search for it on this forum) It's a combination of 250r plates, 400ex plate, cr500 springs, plus washers
3. Any one single step of Cleigh's clutch mod will help.
3. Get a billet clutch basket (the basket takes alot of abuse, the oem tear up quickly)