Is the debt forgiven if the lender forgot?

I recently came to know the seriousness of having debts before dying. What if the situation arises where I borrow a very small amount of money, say the amount equal to the cost of a candy and after about an year or so, if I try to pay him back and if he says "I don't remember lending you any money." In this situation, is the debt forgiven ? Can I keep that money or should I donate to charity?