My bike currently has about 50,000km on it (31,000 miles), so if it keeps wearing at the current rate, I'd guess it would last another 50,000km. But eventually it would need a new driveshaft, which would be a major job.
But it bugs me. It's something that shouldn't wear, it is only wearing because of the way it's held on the shaft.
I was refering to the rotational play when I said there was a fair amount. There is also a fair bit of sideways play, but even a new bike would have that (unless the OEM sprockets are wider than the JTF433-14 sprocket?).