Does giving charity with the intention of paying off a debt for a deceased person, when the creditors cannot be found, absolve the deceased's liability?

Faith is not established by such a dream, as it is not a legal proof. However, there is no harm in taking comfort from it and acting upon it as an act of kindness to the deceased and as a precautionary measure. Thabit ibn Qays's will was executed after his death based on a dream seen by a man, and there were corroborating indications of its truthfulness.

If the heirs act upon such a dream, it is good for the deceased, for either the debt will be paid on his behalf, or it will be a charity for him.

Dr. Khalid Al-Abed recommended that a will seen in a dream should be executed if it pertains to an act of righteousness, provided the heirs consent. If they do not consent, it is forbidden to execute it. However, if the will pertains to an obligation upon him, such as paying a debt or returning a trust, and there are corroborating indications, then it is obligatory to execute it, because these are rights related to the deceased's responsibility, and the dream here reveals a ruling established by the original Sharia.

If the creditor has passed away and none of his heirs can be found, this money should be given as charity on behalf of its owner, and thus your father's responsibility will be cleared if the dream is true.