I believe this case is quite famous and everyone knows about it these days, James Howells lost a stash worth 75 million bitcoins back in 2013, presumably lost somewhere under 20 tons of garbage in England.
http://www.wired.co.uk/article/bitcoin-lost-newport-landfillAs we are unlucky that we probably will never own 75 million worth in cryptocurrency, we certainly are lucky to not have lost it, if in a hypothetical world James Howells had found his hardrive, but it's partially broken, later he find out that it's possible to recover but half of the content is forever lost, in the logic of blockchains can data be "corrupted"? For example he loses half of the money and by a domino effect he ends up losing everything, is that possible?
I love thinking in hypothetical situations.
The two most likely outcomes are that he loses everything, or loses nothing. Either the wallet.dat is corrupted or it isn't. At this point -- in a landfill environment exposed to the elements -- that hard drive is probably extremely degraded. It would be a miracle if the wallet were recoverable.
The guy is still holding out hope that an excavation will be allowed even though it would be an ecological hazard. Sort of a wingnut. The city knows the bitcoins are probably lost.