Hey there, thanks for your question and welcome to the Streamlit community! 
Yes, if you delete your app on Streamlit Community Cloud, your custom subdomain should become available immediately for reuse. You can then redeploy your app from the same GitHub repository and set the subdomain to the previous value, ensuring your users can continue accessing the app at the same URL. This is the recommended approach for cases like upgrading Python versions or resolving persistent deployment issues.
However, in rare cases, there might be a short delay or caching issue where the subdomain isn’t instantly released. If that happens, waiting a bit usually resolves it, but if not, you can contact Streamlit support to manually release the subdomain for you. For step-by-step instructions on deleting and redeploying, see the official docs: Delete your app and Deploy your app. Community members have also confirmed this process works as expected in practice (source, source).
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