Since the Hard Times effects included nukes, planetary bombardments and such, I went ahead and used those rules first, for the Hi Pop and worlds with military and naval bases especially, then came along later with the virus effects and vampire fleets to hit the high tech and whatever ships remained outside the Black War zones and fleet movements.
It does tend to really sink many planets into a real dark age, but IMTU I'm a good ways closer to Core than the Old Expanses and Diaspora on a world similiar to Yontez, only suffering a large Pop loss, but relatively low tech at the start so not all that much affected by Virus, again like Yontez, so it's an 'Up From The Ashes' type that focuses on long term rebuilding while repeling offworld slavers.
I get to use the Twilight 2000 book for encounters, scavenge ruins using the old Aftermath rules set, make good use of the World Tamers book, and can still get offworld for the occasional Swords And Lasers adventure, all in one campaign.