Refund sent to cancelled or expired card
If a refund is sent to a cancelled or expired credit/debit card in most cases, the bank will redirect the refund to your ticket buyer's new or replacement card. If your ticket buyer does not have a new card, the bank will usually send the refund directly to their bank account.
If neither of those options are available, the bank will return the money back to you and Stripe will contact you via email for further action. Once you receive the funds, you can arrange an alternate form of payment for the refund.