If a system is off-site and you delete it from the Core, it will not be able to send an inventory in via the gateway. A system has to exist on the Core before it scan in via the gateway (cloud device).
A system cannot send in a security (vulscan) until it exists on the core... be onsite or off.
If the system connects via a VPN and sends an inventory scan in during that time, it will re-populate on the core.
A system that is onsite will also repopulate when it does its inventory scan.
As MarxTar stated, the first scan might be rejected.... (If onsite or VPN)