I have heard that one can make a transaction which will not confirm before a predetermined block. I am not sure about the details, but the coins will be in limbo for the time being, receiving address will be able to spend it when it gets 1 confirmation in the predetermined future.
So, in essence, one would be hoping that the wouldn't lose their private key in 30 or 40 years? That's beside the speculation as to whether or not bitcoin itself will still be around in the future? I know we all want it to be, but storing huge sums with no way to yank it out if something negative occurs, neither of those seem like especially wise decisions...