If someone stole $5 million dollars and the halacha says you have to pay back 4 or 5 times, that is $20 or $25 million dollars. If he doesnt have the money there is no way to pay it back. Even if you sell yourself into slavery, you cannot earn in 6 years $15 million dollars, you can never pay it back
Even if you stole the $5 million and spent the money and you dont have it anymore, you cant work off the money in 6 years