Even if it didn't affect the Bastion, bringing even one Sathanas away from the Capella star may have bought enough time for all those refugees in the last mission to make it to the node. Had the Colossus not made that distraction the last mission could very well not have taken place.
That's a good point.
Actually I've often heard the idea that, some Sathanases chose to stay behind so that others could leave but I don't think that's true. People have called the Sathanas at times a weapon to destroy stars, while the Lucifer is the planetary bombardment one. But I don't think that's true. When the nova goes off, those four Sathanas in frame don't intentionally stay behind. They're not still doing their green warp the sun thing. I think they're there because of one or two reasons:
1. Making the star go supernova was extremely dangerous. And no, not because "duh, yeah supernova bad" but because the operation itself was incredibly tasking on even the Sathanas and there was no guarentee it wouldn't shut down completely.
2. This fault may be in part due to the extreme age of the vessels, assuming that the Sathanas has been around for 1000s of years.
From the cutscene we see what, 10-11 Juggs? Of those, 3-4 stay behind. Let's assuming 80 Juggernauts, 7 out of 10 make it out. That's a guesstimate 24 Juggernauts that perished in the Super Nova. Not to mention all the non-Jugg forces in system.
Assuming some sort of special jump, that was a one way ticket to someplace REALLY important. I think it's safe to assume that the Shivans would wait for most if not all of the Juggernauts to be assembled before they tried to jump out. So diverting that Juggernaut to waste the Colossus probably did buy all the refugees and maybe even the Bastion a lot of time. But they bought time not from the shivans but from the shivan created supernova.
And the colossus had what, 30000 people? Lets for the sake of argument, assume that an equal number of Shivans are onboard a juggernaut. 24 Juggernauts gone means 720,000 Shivans died in Capella. Makes the GTVA losses seem like a drop in the bucket doesnt it?
EDIT - and as a point of interest, I don't think the final shot in that cutscene of a Deimos and a Moloch overlapping before their death was an accident. Bosch made some waves that's for sure. But that's another discussion.