That is not true. If you've replicated snapshots for monday, tuesday, and wednesday, deleting the monday snapshot on the replication target will not prevent you from receiving a thursday snapshot, nor will it stop you from provisioning a VDB based on tuesday's snapshot. DXFS uses these incremental backups to reconstruct the database just as it exists on the source, but once it's done so, the snapshots are only necessary if you wish to provision from them.