Capitulation would happen over the weekend. It would be best to have the Salamanders or the Ultramarines... the planets brought into compliance by any of the Traitor Legions seemed to quickly be converted to chaos after the start of the HH.
Any military response by our planet would be easily subject to the weapons coming down the gravity well. Nukes could even easily be shot down, assuming the communication infrastructure survived long enough. World leaders could be captured/killed in short order using teleportation technology, regardless of how deep the bunker was located.
I'd also have to wonder how the more religious among us would respond when they encountered their first Librarian? Either way, after the civilian governments capitulated, their first order of business would be in hunting down the religious resisters themselves for fear they'd trigger reprisals against the general civilian populations.
The White Zone is for loading and unloading only. If you have to load, or if you have to unload, go to the White Zone. You'll love it... it's a way of life.
: Cigarettes in space?
: It's the final frontier, Nick.
: But wouldn't they blow up in an all oxygen environment?
: Probably. But it's an easy fix. One line of dialogue. 'Thank God we invented the... you know, whatever device.'