If you cancel your subscription, you’ll still have access to your Splice subscription (including your credits) until the end of the current billing cycle. After that, you won’t be charged again by Splice, and you will lose access to any remaining credits on your account. Your remaining credits will expire 28 days after the end of your final billing period, so you'll have until then if you wish to resubscribe and reclaim your credits.
After cancelling, you can continue to use the Splice desktop app to access and browse your sample library. You can also re-download any previously-purchased samples that are already in your library, but again, you will not be able to download new content from Splice without an active subscription. The certified license for the content you’ve added to your library is yours in perpetuity, even after cancelling.