You keep your refund. Once a premium credit has been returned to you, a late response from the curator doesn't reverse it.
How the timing works
Premium credits auto-refund when your campaign expires, roughly 72 hours after you submitted (48 hours for influencers). If a curator hasn't given a valid response by then, that credit goes back to your balance and stays there. See the "How do I get a refund for a submission?" article for the full list of what triggers a refund.
If the curator responds late
Sometimes a curator gets to your song after the window has closed and approves it or leaves feedback anyway. When that happens:
Why it can look like something reversed
A late approval or share still fires the usual notification, so you might get an "approved" or "shared" email after you were already refunded. That's just the notification catching up to the curator's late action; it doesn't undo the refund. If you're ever unsure, check your credit balance: the refunded credit will still be there.