Blob files won't get deleted automatically. You can save files as long as you want. You will have to delete them manually when needed or they can be deleted once the lifecycle has ended based on the - Lifecycle management rule created.
If you want them to be deleted automatically, you can explore lifecycle management rules to move the blob to different tiers
Below documents should help
https://learn.microsoft.com/en-us/azure/storage/blobs/storage-lifecycle-management-concepts?tabs=azure-portal
https://learn.microsoft.com/en-us/azure/storage/blobs/storage-blob-storage-tiers
https://cloud.netapp.com/blog/storage-tiers-in-azure-blob-storage-find-the-best-for-your-data
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