User blog comment:Collbrande-Ex-Caliburn/Hyoudou Issei's Peerage composition hopes/dreams/hypothesis/@comment-10330822-20161112235347/@comment-9595671-20161122200147

Actually that was in Volume 12, and they fled to the Khaos Brigade once they were caught. Also, by that point in the story according to the Fallen Angel's page, there's now a decreasing rate of natural-born Fallen Angels. So they likely can't just rely on reproducing normally anymore.

It was also said the 1st through 6th Heavens were only devastated and prepared before the last battle, I doubt this use of devastated meant destroyed for 2 reasons. The first is no one except the Seraphs can enter the 7th Heaven, so the surviving normal angels wouldn't be able to relocate there if the six got annihilated. The second is for the same reason the Evil Piece's system needs to be intact, without it... many would die.

The Evil Pieces' system is in Hell, so the Bave Saints' it's most likely in Heaven, probably the 5th Heaven since that's where the research is done. Irina and Dulio are still OK, and there doesn't seem to be any problems with them. As for research data?

Since Trihexa didn't attack until few days after it was free, and everyone knew they'd have to fight it, I bet Heaven made sure to either move or send copies of their research in case something happened to the system when it finally came to attack them. They knew they wouldn't win and they'd take heavy losses, so they likely had to use that time to try to protect and save the most vital things they could, especially while Issei was out of action.