How can the price of gold that was sold to secure the release of a debtor from prison be repaid after the creditor's death and a change in the price of gold? Is it at the price at which it was sold, or at today's price?

What you did—disposing of the trust (amanah) without its owner's permission—is a sin that necessitates repentance and seeking forgiveness. Allah the Almighty has elevated the status of trust and linked its betrayal to the betrayal of Allah and His Messenger. The Ahadith also encourage safeguarding trusts. Furthermore, the trustee becomes liable for what he spent the moment he infringes upon the trust. Therefore, he must pay the equivalent of the gold he disposed of to his colleague's heirs. He should only pay the price with their consent, and the payment must be exchanged at the very same moment.