From 11.19, we block deletion only when mount path has any data.
View contents on mount path may show no valid data but it may contains dedupe data referred by other jobs. so check for physical direcotry contents and see if there is no data then you should be allowed to delete even if DDB is active.
Before 11.19, you need to seal DDB and wait for all data to be pruned.
We never block deletion if storage policies associated with subclients.