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So if the price of BTC reach $60k in 30 years, you will not sell your BTC? Don't you know that many people will sell and save the money and wait for the price to decrease before they can buy again to wait for another bull, and before that 30 years the price of BTC will reach $100k he or she has made a huge amount of money. What about some bad happen that may lead to death, but we don't pray for such thing to happen but is a something that can come at anytime as long we are human, and you know that many BTC holders don't use to share their wallets detail to their children, wife or husband based on past experiences, so if you hold like 25 years hoping that the price will reach $100k and the price manage to hit $65k and you continue holding and something happen, what do you think will happen to your money.
I understand what you're worried about - but every investor or holder has probably thought of their own way out including inheritance.
If you can be a bitcoin holder for over 3 decades - then why don't you? The problem here is not when you take profits - but how you manage the risk of your investment as long as you don't want to sell it for financial or other reasons. It's true that it's always good to sell at a profit instead of holding on forever - but all of us are not the same.