What happens to a ticket purchase with an e-credit/eCertificate if refunded?

Hi, hoping to get some clarity here since I couldn't find a Delta policy. I have a eCertificate expiring soon. I don't need a Delta flight at the moment. What would happen if I use the certificate on a refundable flight, or cancel within the first 24h? Will I get a new certificate with a later expiration date, or does the credit go back on the initial one? Any input, would be greatly appreciated! Thank you.