Upon the death of the certificate holder, the bank will handle the certificate as part of the estate according to the legal documents of the heirs, not using an old power of attorney or the deceased's ID card.
Key points
Officially notify the bank and inquire about the status of the returns up to the settlement date and the options for continuation or redemption, depending on the product and procedures.
The existence of the certificate does not negate the rules of inheritance or the establishment of heirship.
The figures, fees and limits in this answer vary by bank and change over time — confirm them with your bank or the official source before acting.