An Azure service that provides an event-driven serverless compute platform.
Given the lack of source control, Azure backups, or retrievable storage account data, recovering the deleted function is highly unlikely.
If the function app was hosted on a Dedicated app service plan, it can be restored, as long as it was using the default App Service storage. See:
https://learn.microsoft.com/en-us/azure/app-service/app-service-undelete?source=recommendations
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Regards,
Abiola