Let's say bitcoin has been widely adopted, the wallet.dat containing Bill Gate's net worth crashed (because his misplaced faith in Windows) and there's no way to recover the file; his foundation need this money to pay 10 million children's medical bill -- in another word, there's catastrophic/extraordinary consequence if the money cannot be recovered -- should there be a mechanism to deal with this kind of situations?
It's called backing up and encrypting it.
To add what kiba is saying, I would also suggest that (out of fear of assassination) Bill could encrypt his wallet with multiple keys such that his backed-up wallet could be decrypting with the combined requirements of (1) a cryptographic confirmation code for Bill's death certificate issued by his specified hospital/DRO/court/insurance provider, (2) one or more keys (depending on the specific terms of his particular will) of Bill's heirs, (3) Bill's lawyer.
Or for this case described above, I would think Bill's 10 million donation would be put in some sortof escrow, whereby there would be specific mechanisms (think *smart contracts*) where the money could be dispersed automatically in monthly .1 million increments. No need to keep a human around, right? Cut out the points of failure from dumb human operators.
sorry but the dumb operator has been backing up the wrong file ... a low probability event, just wondering what if it really happens.
Sorry, but a dumb government operator just pressed the red 'nuke' button accidentally.
Sorry, but a dumb government person just lost the physical key to the US Bullion Depository.
Ok, but seriously, we can do a thought experiment. If some rich dude's gold stock pile suddenly disappears from the face of this earth (by some black hole or anti-matter), then what happens? Well...obviously that rich dude wouldn't be able to spend as much, so the overall aggregate demand curve for society would likely decrease by a small amount. This would cause the equilibrium supply-demand price point to drop a very small amount for all goods in society that that rich dude would have demanded.