Is it permissible to delay returning excess funds received from a government entity and lend them to a friend in need, knowing the difficulty of securing them again if demanded?

The questioner must repent and return the salaries that were disbursed to him after he left work, because it is money he is not entitled to. His liability is not discharged by transferring the amount to his friend, unless the entity will not dispose of it lawfully. In that case, he may spend it on charitable causes and public welfare.