In a situation such as this one has to ponder the given facts, or complete lack there of;
1)The Captain of the Collossus chose, againt direct orders, to stay in the field of engagement to "buy more time for the Bastion", his EXACT motives will remain a mystery, so whether he did it to stall the Sathanas just those 6 extra seconds, or stayed there so the Shivans wouldn't have sent another Sathanas to get him, we just don't know...
2)We don't know the motives the Shivans had in creating the Subspace Field around Capella, thus we don't know if all the Sathani were need, ergo, we cannot say exactly whether or not the Shivans would have sent another Sathanas to deal with the Collossus threat has she chosen to jump.
3)We don't know exactly the Fleet Resources the Shivans had in-system at the time, meaning we can't simply say "why didn't the just swarm the Collossus with Ravanas and such", as we don't know if the Shivans even had that many Destroyers. We don't ever get an estimate on the size of the Shivan Armada past that of the 80 Sathani, and thus cannot base any arguements on that of the remaining Shivan Presence in the System beyond that of the 80 Sathani orbiting Capella.
4)The only thing we DO know is that the CO of the Collossus did indeed give the order to his crew to remain in the firing line of the Sathanas. We know that this action cost the lives of 30,000 Crew Members, and it likely saved the Bastion (evidenced by the fact that her mission did indeed succeed). Thus, one can only conclude that, whatever her Captain's motives were, the Collossus did indeed do the right thing in staying there, shown by the fact that the Human & Vasudan races still exist.
So really, someone shooting down another's theories based on their own theory, which is in turn based on other completely unsupported theories (such as saying the Shivans definitely wouldn't have sent another Sath because they probably needed all of them at Capella itself), well, it's just plain not nice. This should be about shooting out our own ideas and building upon them, not putting an idea on the table and simultaneously shooting down another's as completely wrong...finally, my apologies for rambling...