From Lexicanum

the planet is not destroyed it still exist

Well it is clearly listed as 'destroyed' in Codex Dark Angels (4th Edition) page 73, and in Codex Space Marines page 8. I think that you are mistaken. Irulan 18:02, 26 April 2008 (CEST)

well then if it was destroyed how did the Adeptus Mechanicus find schematics of the Terminus Est

User:Emperorspartan 11:50 am august 05 2008

The description for the Despoiler Battleship says the plans were found in the ruins of Barbarus. Thus, hinting at its destruction.