Currently, BBMS retains and continues to process credit/debit cards that have expired for up to six months, provided that the card is still honored by the issuing bank. At that time, the token is discarded. For monthly donors, this means that by the time the recurring transaction fails, the token is gone. If the card number is still valid and you only need to change the expiration date, it's too late; you have to get the whole card number again.
A better method would be to keep the token around for a while (at least a week, maybe even a month) after the first rejected transaction.