How can one act regarding the theft of a sum of money from the father, given the current inability to return it due to unemployment, and the fear of it remaining a debt until the Day of Judgment?

Theft is forbidden and is one of the major sins. However, if it occurred before puberty, there is no sin upon you. You must return the stolen item or seek your father's forgiveness. It remains a debt upon you until you are able to return it, or until you seek his forgiveness and increase your kindness and good treatment towards him. It is not permissible to describe your father in an unfitting manner, nor is it permissible to steal from his money as long as he provides the obligatory maintenance. It is permissible to take from his money an amount sufficient for your needs if he falls short in providing the obligatory maintenance.