My own thoughts on this little idea.
Following such a cataclysm, both the SLDF and House's would rush in assistance, including troops, pretty much throwing a big spanner in the works of any Republican plans for a stab in the back. I think the idea of a compartmentalised attack is probably true, so apart from a few high ups in the RWR, who are just as out of touch as anyone in the Hegemony and would miss the window to launch the attack, no one in the Hegemony would know what Amaris really planned
With no Cameron’s, the old fight for the throne, starting with bickering and degenerating into war would still happen, even with whoever the Hegemony finds to rule. Not being a Cameron, the other Lords would only see them as Director-General, not heir apparent to the Star League.
With things falling apart, the SLDF would fracture, but the TH would likely come out best, with far more complete formations staying loyal to Terra than any other particular state.
The war in the Periphery would wind down quickly, not causing as much damage as before, but the RWR, with all the extra toys, would become a real player in the Succession Wars. Instead of a 6 way bout, I would see a 7 way bout with the Taurians and Canopians being bigger players than before.
However, with the SLDF so much stronger than before and its troops and ships across so many states, the 1st SW is going to be EPIC!
Even if it is just the TH/SLDF trying to bring the other 5 idiots to heal, because even if the SLDF fractures, the Hegemony is going to have one hell of a force.
That’s my 2 cents.