How long on average does the drive sprocket and chain last. Have 20,000 miles on a 03 Honda Shadow 600

That all depends on the quality of the chain and how well its maintained... cheap, non-O-ring chains wear quicker and stretch more... high quality name brand X ring chains properly maintained can easily have 5 times the life or more.

As far as sprockets.. its much the same... worn chains accelerate wear on sprockets..

Here is a good writeup with pictures

Motorcycle Drive Chains

Thanks Smoothy. Very helpful link.