Thank you for posting. The WVC210 does not have an overwrite feature and will continue to send video until the destination drive is full. The software has the ability to control this of course, along with much more functionality.
If you map a drive to the NAS and record to that drive the software should work the same as if you are recording to a local drive. The software needs to be running in order to overwrite or delete the old files. The hard drive or NAS will simply store them until told to do otherwise by the software.