How can one repent from theft and the expenditure of ill-gotten gains, given obstacles to returning rightful dues to their owners, and what are the implications of that regarding zina (unlawful sexual intercourse) and repentance from it?

Theft is one of the major sins that necessitate the cutting off of the hand in this world and torment in the Hereafter, as Allah Almighty says: "As for the thief, male and female, cut off their hands as a recompense for what they earned, a deterrent from Allah. And Allah is Exalted in Might and Wise."

The thief must return the stolen money to its owner, according to the hadith (definition): "On the hand is what it took until it returns it." If the amount is unknown, one should strive to estimate it to clear one's conscience. The money can be returned indirectly without informing the owner if harm is feared.

As for the injustice of the employer, the governing factor is the contract between you. If he gave you the agreed-upon wage, he did not wrong you, and his promise of a bonus is not binding. However, if he withheld a wage due to you by contract, then it is permissible for you to deduct it.