The lifespan of the WP in a 986 is variable, and it is not on any official maintenance schedule. There is no way to really determine when they fail, the average life from what I have seen appears to be in the 60-80k mile range, with some failing sooner and some lasting longer.
That said, it is best to replace them before they fail to avoid either impeller bits in the coolant system or boring a hole into the engine casing. It's completely debatable, but the suggested preventative WP replacement seems to be in the 50-70k mile range. I had mine replaced under warranty at 30k miles, I replaced it preventatively at 95k, and I will replace it again in 60k miles, assuming I am not experiencing symptoms of a WP failure before then.
