@lipintm
ANY unpaid debts of a person when they die are suppose to be paid out of their estate by their executor. If they have no Will, various state laws govern the process and a personal representative is appointed to handle the matters.
As to your 1st example - when the death certificate is supplied to the credit card issuer, they will make an attempt to collect from the estate - if no estate, the authorized user could be on the hook for all charges but specifically for those made after the date of death.
Again, in your 2nd example - the estate of the deceased will be paying for the balance remaining on the credit card or if his wife was on the account as a joint holder or authorized user, the party left standing is responsible.
Creditors of all type know what to do to collect in most instances. There aren't really any loopholes for honest people.
It's Always Something . . . . Roseanna Roseannadanna