If a resource such as a Computer, Package, User, Site or Subnet is replicated down the hierarchy, will this resource be deleted at the child NS on subsequent replication if the resource is deleted at the parent NS?
No, only Configuration and Management Items act in this way. Replicated resources, Events, and Security objects (such as Security Roles and privileges) do not.
Examples of Configuration and Management Items would be; Reports, Policies, Tasks, Filters, Targets.
So if the user at the parent NS creates a new report, and replicates this report down the hierarchy. Later the user at the parent NS deletes this report. The next time Item replication via hierarchy is run, it will delete this report at all child servers. This is expected behaviour.