Is it permissible to pay off a debt on behalf of a deceased person through charity in a mosque or to an orphanage, in the name of the creditor, when it is impossible to communicate with him or his relatives?

If the deceased has an estate that covers his debt, or part of it, then the heirs must search for the rightful claimants or their heirs. If this becomes impossible after due effort, then they have the choice between handing it over to the judge or giving it as charity on behalf of the rightful claimants, while guaranteeing their rights to it. The reward for the charity goes to the rightful claimants. This charity may be for building a mosque, sponsoring orphans, or other acts of righteousness. However, if the deceased has no estate, then the heirs are not obligated to pay his debt, but it is commendable for them to do so.