Yeah, that's true and it's actually one of the few things that is inevitable, whether we like it or not , a certain number of Bitcoin owners are actually going to end up leaving this world with their key remaining unknown to anyone, even their love one, but I feel this is supposed to be a matter of who's going fall under this category, well I know for sure after all this exposure to this much knowledge, I will definitely find a way to let my love ones or even my spouse know about the my holdings or if that's too wild, I think setting up a means of which they can actually get hold of my key and Bitcoin when mr.death eventually comes knocking.
Do you know what most people who are holding bitcoin are doing or will most probably do? All of them know that they will transfer their private keys to their loved ones when they are near to death but no one will let the keys be transferred ahead of time. Since the death time of everyone is unknown, there may be many who die because of an accident or on the spot death and they would not even get the time to give the private keys to their remaining.
Since bitcoin is very new and only the first generation is using it, so we do not come across such cases but after more than 10 to 20 years, a lot of bitcoins will be lost as the current holders of bitcoin wouldn't be alive and they have not transferred the wealth to their near and dear ones.