[@6slyboy6] That would depend on situation, The Black Sun still want to become their own entity separate from the Empire away from the prying gazing eyes of the Empire. While it's true that the Emperor provides a good living for the Humans, some brighter minds (Somewhat like Tunis) have thought that one man on top of the hierarchical chain should not be the sole decider for the entire Empire's fate because at the end of the day it is still the Emperor's call.

The situation would be either (keep in mind this is assuming they haven't seceded yet)

A.) The Empire and the Black Sun are forced to work together (I.e. The Xeno's decide that the black sun is just as bad as the Empire)
B.) The Empire somehow reformed into something the Black Sun would like (I.e. Establishing a Parliament and getting rid of the Theocratic ways of the Empire or something similar)
C.) Propaganda (Would be effective for a sum of the Black Sun's forces and would require some story if it involves any of the main Characters of the Insurrection)
D.) Force the Black Sun back into the arms of the Empire.

If they have seceded then there would only be a couple of options

A.) Form a treaty with the new Human Government that would separate from the Empire.
B.) Force the new Human Government to it's knees.
D.) Propaganda (This would be even less effective than if it were to be before Secession as counter propaganda would be more prevalent)

However, even if these options sound very narrow, it's because the story hasn't really progressed, this is how I see things shaping up, and I don't deny, it might be fun working with the Empire. We'll see...