Well, assuming the party survived the firefight with the eldar.
They would have explored the rest of the structure and found.........
.......after the flight to the Righteous Fury with those that has survived the.........
.......returning back to footfall battered and broken........
The above would have been a good result
Also, the nid fleet attacking the Calixis sector would have been destroyed by the obvious but in turn Castagirs chapter system would have been destroyed and the beginning of the end started that would have finished within some of the pc's life spans