There's a theory that says if you can pull a link away from the sprocket at the rear of the chain that it needs replacing. At 16000miles I'd definitely be looking at replacing at least the chain. Have a good close look at the teeth on the sprockets - if they're the slightest bit hook shaped they need replacing too as putting a new chain on worn sprockets will just kill the chain. If you're replacing the rear you should replace the front too - it's a much smaller sprocket so for every turn the rear does the front does several which means it wears a several times the speed of the rear.
When I did mine I found a company that laser cut the sprockets instead of buying an off-the-rack set - they're lighter, better cut and harder, and it gives you the opportunity to use slightly thicker sprockets and a thicker 530 chain instead of the standard 525, which increases the life of the chain significantly. 530 links are the same length as 525 ones, just wider.
Think of it as an excuse to get an 18 tooth front sprocket, if you haven't already.
