Most of these systems are not actually reversible at the protocol level. They sometimes offer cancellation at stages prior to settlement. When needed, transactions are most often "reversed" at the governance level.

Bitcoin is reversible on the same level then.

If someone dies with their bitcoin password locked in their head, you can't get the account passed to whoever is named on the will, the coins are locked forever.

Maybe a smart contract could help here. If there are no transactions on a wallet for more than some time period, allow the wallet to be unlocked or transferred to a trusted party.