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There's no reason I can see that the lack of a Federated Commonwealth would prevent the Dragoons and Dragon from falling out, and with Takashi having something to fixate upon, I could see Hanse relying on the Dragoons (with more reinforcements than in canon) to keep the DCMS busy while he tears into the Capellan Confederation. He has Justin in place so events can reasonably be considered to be favourable.
At this point Hanse has cut the Tikonov Commonality away from the Confederation, with reasonable odds of convincing Ridzik or someone else to rule it as his puppet. He has Tikonov itself as well as several less important industrial worlds. The CCAF is too badly hammered to prevent him from consolidating his position, particularly since the Free Worlds League is virtually guarenteed to be putting pressure on their borders.
One advantage that Hanse would be lacking is his marriage- his wedding was a part of the diversionary plan for the 4th SW- just as much as Galahad. Without all of the house leaders on Terra and away from their capitals and military commanders would their response be as slow? Would Hanse's surprise be as complete? I think with out the wedding lulling the other house lords into believing that their would be no major military action Hanse doesn't catch the Capellans completely off guard.
That's a good point- without the FC there would be no Treaty of Kapetyn and no reason why the FWL would not attack the CC.