An interesting article I just ran across:Funny you should mention that... I was wondering if it was still sqwaking after all these years. I thought I heard years ago that was almost out of range then.
It agrees with what I recalled from a number of years ago -- that, barring the very likely failure of the transmitter before then -- we should be able to continue receiving diagnostic signals from the craft for more than 50 years after it's launch. Whether it will be worth the opportunity cost to do so once the last scientific instrument is silenced is a different question. I imagine at that point they will only listen occasionally just to put a close estimate on when she finally falls silent.