If you place a Click + Collect order and it is no longer available in your chosen store the store will reject the order and notification will be sent to you advising same by email.
The order will automatically cancel and the payment will cancel with it. All orders, once placed, have a pre-authorization hold on the payment. If the payment is made with credit or debit card the funds may take up to 3 business days to release back to your account.
If the payment is made with PayPal this will void on the system immediately and release the funds back to your PayPal account.