Can stub objects be included into publication and published back into original object's forest?
Publishing stub objects back can create multiple issues including synchronization loop and is not supported. It is possible to turn stubs into regular objects and publish them back only when original objects are removed from the publication at the publishing forest. Please see Resolution for more details.
Stub objects are tracked by "ACS:" address in the proxyAddresses attribute, so removing them from QCS OU and cleaning up these addresses will satisfy requirements of turning them into regular AD objects. If original objects are no longer included into any publications, this will exclude any possibility of synchronization loop and such stub objects can be then published back into originating forest.