I don't think the jumpnode collapse plan proves anything. First of all, it may not work. Their efforts at Knossos subspace portal was a total failure. The baston was nearly destroyed before entering into the node as well.
They blew up the Knossos in Gamma Drac, not the portal. Big difference. The Bastion actually succeeded, and there's some indication in Petrarch's speech that the Nereid succeeded as well ("We sealed of Capella and our people are safe, maybe forever.") Also, Nereid came from Vega, not a Shivan infested system like Capella, and the Shivans never got beyond Capella.
Even if it did work. the shivans are known to be able to open new nodes and/or use uncharted/unstable nodes. Thereofre, the plan is far from fool proof.
All we know is that they used routes unknown to the GTA-PVN in FS1. Those were probably unstable jump nodes. However there's a difference in unstable jump node and destroyed jump node. Detroyed jump nodes can only be reactivated using a Knossos. Yes, the Shivans probably have that technology, so the plan is far from perfect. It is only good as a temporary solution. (and we need the Shivans coming back for another visit in FS3)
But now let's add a supernova to the equation:
a) the star is no more. It's gravity field is no more. You need a sun's gravity for a subspace node*. The shivans therefore did exactly what the GTVA was doing. They sealed off Capella.
b) the new nebula will be quite inhospitable even for Shivan ships for a few hundred or thousand or even more years. (altough
might conveniently forget this and allow ships in the nebula a few years later)
The Shivans actually made their job more difficult. They sealed off Capella for a long time (because of b)), while the GTVA would've sealed it of for a few decades. (until the shivans come and build a Knossos).
The destroying of the Capella Sun simply doesn't add up
I recently spoke to someone who finished FS2. His first question was 'Why did the Shivans blow up Capella?'. It does not add up, and this was
's intention. They didn't want just another 'the Shivans come, they kick ass, we're almost dead, but then we discover a way to save our butts (sealing off Capella), and we survive' type story. They added a huge cliffhanger because they wanted players to ask exactly this question, and then buy FS3 just to get the answer. Even if they made the worst space sim and named it FS3, it would be bought by us, who played FS2.
*This is probably not canon, but the only nodes we know of are between two systems. It would also explain why there were Knossos portals in Gamma Drac, the Nebula and the binary system. No sun (& it's gravity field) in Nebula -> No connection to Gamma Drac and Binary system. Sun and black hole in Binary system messing with gravity field (unsure about this one) -> natural nodes can't form
Well, someone in FS3 would have had ships 'large enough to have a gravity well'*.
*paraphrase
Option 1: The GTVA builds a Death Star* and the Shivans, of course, have something bigger
Option 2: The shivans have a huge mothership (it would be like the Lucifer in FS1)
*Babylon 5 is 5 miles long, a bit longer than the Colossus (8+ km), and has a gravity well around it, enough to keep a human body from drifting away if dumped from an airlock ('And The Sky Full Of Stars' IIRC). <length of colossus> / <length of Orion> = 3. <length of Colossus> * 3 = 18 km.