Best solution in this not-so-nice-universe would be to do what n00bl3t said, sleeparrrr ships.
I mean, we did it once...
On another note, the Nomads of Sirius appear not to be able to get their massive sun imploding thing, suggesting that they are not the same as the ones in Sol. Considering that the bonus dvd (Courtesy of Treewrym) shows concept art for the intro sequence and a pilot of said vessel, it suggests that they are indeed a different group.
What has come to be a commonly accepted view of the Nomad's reasons for wanting rid of humans in Sirius is this:
It's theirs.
They were born in Sirius which is in itself, a playground to learn in. Valhalla 1, Cardimine, Gallia planets etc. All of these are not normal things to appear in random parts of un-inhabited space.
The humans in Sirius came from Sol.
They are like a group of Gypies/Tinkers/Travelling Community folk moving into your house when you are asleep and then when you wake up, they refuse to leave.
You can't go to a higher power, you can't call the police.
YOU have to deal with them.
Which is what the Nomads are doing.
All conjecture really though.
Anyway, Kusari would fall, Bretonia next. Liberty and Rheinland would probably turn on each other, courtesy of the Nomads. In the end they could be used by the Nomads to help their expansion (Energy sources etc) and generally do certain things the Nomads would prefer not to use their time on (Needed but not as needed as other things etc)
Last hope would be running away.
Again.
