(imported comment written by Lee Wei)
If you delete the unmanaged assets, and you rescan, yes, they will populate the repository again.
They repopulate with new IDs, not as the original assets.
When you remove unmanaged assets from the Console, they are marked as Deleted, but not actually removed from the database.
So you can indeed undelete them from the UNMANAGEDASSET_ASSETS table in the BFEnterprise database.
update unmanagedasset_assets set isdeleted = 0
where isdeleted = 1