Sanguine, there is always the option that we don't attack them (ooRP or inRP). "Broke away" might be a bit strong but you can work out what Inferno means. They'd be classified as closest to indy miners, who we can't pirate. However, as the 'more lawful part of the Guild', IMG| wouldn't bother - only taking action when they actually cause trouble for us (which going to Humboldt greatly decreases the chances of happening).
Even then, when was the last time we ever pirated BMM, Kruger or Daumann after the turf wars? There are already plenty who do that. Try not to represent the IMG| as the aggressive territory-claiming group it used to be with full Colonial support.
