There are several resasons a deleted computer resource may reappear in the console. THe following are ther three most comon.
The solution for all of these reasons (and most any other reason) is to follow the following steps in order.
Actions > Discover > Import Microsoft Active Directory.
Actions > Discover > Import Domain Membership/WINS
Actions > Discover > Network Devices
Actions > Agents/Plug-ins > Push Symantec Management Agent
> Scheduled Push to Computers Policy.