I hope the person you mean is not Satoshi Nakamoto, because he will never touch the Bitcoin in his wallet ever. Different cases may happen to the people you mean, many events that were never expected before can make them no longer able to touch their Bitcoins. Common cases occur due to loss of access to open the wallet and death of the original owner.
If the wallet with Bitcoin stored in it can no longer be accessed by anyone, then the circulation of Bitcoin will decrease. It is necessary to educate traders or investors who are just starting to invest in Bitcoin to always protect or store their private keys in a safe place, because if they lose access to open their wallet, their assets will be frozen forever in that wallet.