By any account, the battle for Capella was lost upon the sighting of the third Sathanas. There was simply nothing the GTVA could do to stop a second or even a third--the Colossus was quite banged up... even if you kept the Big C at highest hull strength, she went around for a rampage and got battered up from that as well. By the time they saw a second Sathanas, the GTVA was very afraid. That's likely when they started drafting evacuation plans for every system, starting with another evacuation of the Nebula and followed by all systems! The GTVA would have no idea what the objectives of the Shivans was to be this time... they probably thought that the Shivans were headed back for Sol after laying waste to each and every system with multiple Sathani.