80% of the demonetized currency was back into the banks, 20 days before the final date [0]. Bloomberg reports that the final number could be as high as 97% [1].
Now, the question you should ask is - How much of black money was in cash? The answer is approx. 6% according to Min. of Finance White paper on Black Money. So, effectively - 86% of the currency was demonetized to target 6% of unaccounted income. No matter how you slice/dice this policy, the costs significantly outweigh the benefits.