20K miles: how this chain looks like?

[GoldOxide_imp]

I have never worn down sprockets like some folks seem to do (especially if the bike is taken off-road riding), but depending on your standard of care and maintenance, I would think an owner could get over 60000 kms out of the chain (sprockets likely more).

I have used non-o-ring chains past 75000 kms without needing a change and the sprockets were pristine.

Again, your mileage will vary.