But it does depend on a number of different factors.
If you don't remove the Computer's record from the NS and you don't have purging turned on the NS will never know the NS agent has been removed, it will still think it's got an agent and so won't appear in the default target for the Scheduled Push policy. However, if you delete the record or have purging turned on to delete records and it gets discovered again then it will get pushed to again if your Sheduled Push is set to the default target.