A rough guess of mine will be from a 100-1000 btc from what all stories I have heard about and maybe, maybe there is more that is under the earth for which there is no claim for. A lot of people have started to regret this after the price went up massively and they now don't remember where they kept their bitcoin or what was their login credentials to their account or some other reason. Can people not be more careful? Do this once more then you will regret even worse.