Cartridge Life

I have had a Linn Arkiv cartrige for about 5 years. It has be well well cared for and not abused in any way. I estimate it has about 2,500 hours on it. It still sounds fine. My questions are -- How long should it last? What telltale signs indicate the need for replacement?
...with proper maintainance another 2.500 hours at least.
I've heard as little as 1500 hours if you're not using stylast... you might want to have it looked at to see if it has flat areas near the tip.