As per Arun Jaitley, the demonetised cash in circulation on the 8th of November was 15.4 lakh crores. The population of India is over 120 crores. (been six years since the census, but we go with this lower number). This averages to 12,833 thousand rupees per Indian. It may seem a lot, but the money is always circulating and held in larger numbers with banks, organizations like railways, governments, hospitals, supply chains for various goods, safety stashes of people at home and wallets of people who got paid in cash (8th November was after people got paid - usually in those notes) and relatively well to do people.
It doesn't seem like an excessive amount of money to be circulating for a country our size that operates mostly on cash.
How many notes really would be circulating out in the open for people to hoard? Sure there would be some. But we already have reports of large scale laundering with reasonable claims of it being linked to the ruling party, so we can count that as "inevitable". How many stashes of cash would be left with gullible people at all?
It is no surprise that banks are saying that it looks like 90-05% of the demonetised notes will return, showing that there wasn't a lot of black money as cash at all. The government will hurry to claim that whatever didn't come back is black. But at least some of it would simply be notes that got destroyed or lost. For example the Uttarakhand earthquake with thousands of tourists dead taking their cash with them, buried in the rubble. Fires in markets and such. Old people with emergency cash they forget about that will eventually be found somewhere in the home in forgotten purses and hideouts under shelves. It would probably not be a huge amount, but such notes would also be among those that don't return. And notes will continue to return to the RBI for a while yet.
At the end of the day how much black money would have been defeated by forcing enough citizens to rival with population counts of moderately sized countries into queues? What would be the resulting monetary boost the country will get? Will it even cover the money the country spent as toll waivers and printing new currency and distributing it and expenses incurred by banks? Can it even begin to cover the losses forced on citizens with this stunt?
From the sound of it, not much black money will be found. I'm willing to bet the total amount caught may be less than the income of a couple of individuals in the country.