Whatever, but if I understand you correctly, that still doesn't the situation for the great grandson right? He finds the chest with 100 million USD worth of gold after 110 years and it is not his anymore? Whether someone + their successors arbitrarily decide to keep it for more than 109 years or whether is lost doesn't matter? I mean what if I just don't want to sell but keep it as part of my diversified portfolio? What happens then after 109 years?
Bitcoin can also be noted in mBTC and satoshi. I am confident that whatever gets lost over the decades to come, there will always be enough satoshis so serve Bitcoin's purposes.
It is not that I don't get the problem you are describing, but it is a very delicate topic as it goes straight to the core fundamentals of Bitcoin which as of now essentially are the value proposition.
A wallet can "verify" its activity with a single transaction. One can preserve his coins just by verifying once every 131 years through a simple transaction with the given wallet. This will state to the protocol that the wallet is still "alive". If the wallet doesn't make transactions after a period of 131 years, the wallet will be stated as dead by the protocol, and the coins recycled into the network.
There is no threat to holding coins, nor to keep diversified portfolios, or threats to legitimate inheritance.
But is there any other asset class apart from things like copy rights or patents where you have to refresh ownership or verify that you are still alive and an active owner of a certain asset in order to not be expropriated? It is still quite a special situation that you are describing here. I get the idea why you say it could be important to recycle coins into the network, but why would Bitcoin be treated as a non-durable asset class? Everything else is. If I own a gold bar I won't ever have to go anywhere and prove continued ownership nor do I have to signal or verify anything ever. A piece of art also doesn't become worthless just because it has been lying around in your basement for 200 years.