Re-importing a contact that was deleted

Hi, What happens if I delete a contact and someone re-imports that contact using an Excel sheet or something? Is the contact re-inserted? I'm asking because I'm trying to clean up our list by doing the following: 1) Identifying everyone that has unsubscribed and is subscribed to no list 2) Running a campaign to ask people who have not unsubscribed, but are not on a list, to subscribe to a list or to unsubscribe completely 3) Identifying hard bounces and removing them As part of (2), I was preparing to delete the contacts that had unsubscribed when I noticed that someone in our organization tried to re-upload unsubscribed contacts (and others) using an Excel sheet. So I'm concerned that if I delete unsubscribed contacts (no matter by what method) they could be re-instated against their wishes. Is that the case? Thanks, L