So you (or your wife) want to cancel the card, not even pay the anual fee and still get 20,000 miles? Even if somebody did that successfully before, it's clear that the bank has the right to withdraw the miles in a situation like that. Now what would happen if your wife had already used those miles (and had less than 20,000 miles in her account) I don't know, but I think it's not worth the risk trying.