Around a dozen noble houses survived the destruction of the Aegean Hypercomplex, along with several hundreds of thousands survivors from all branches of military and civilian sectors (from a population in the billions).
For 60 years after the destruction of the Ageans, Imperial survivors battled Ork survivors. The Minos, Crassius, Macharius, Westguard, and Ithacaran noble families based from the Kalrek Voidstation were able to help hold things together with strong leadership.
With no links to the rest of the system, it was unknown whether the greater war was still going on. survivors lost sight of the large picture and simply battled for survival day-by-day.
Both sides picked through the chaotic ruins of the vast space-industrial sector as it settled into stable gravitation pockets on the edge of the Warp Rift that became known as the Scylla Reef.