The plot is just incredibly overcomplicated and needlessly risky. Both the king and the privy council didn't want the prince to disband ACCA, so they could have easily just stripped him of his position and let somebody else be king, or just transform the position as ceremonial. Hell, why not just have a private talk with the prince, was the public demonstration even necessary?
Everyone knew Lillium was up to no good, so why not directly do something about that? Beside they end up disbanding the 5 council anyway, why not start there? Lilium would have lost all power. Or Jean could have just ascended to the throne and then made his position ceremonial or disband the royalty, or hell, just say no to Lilium:
Lilium: "Jean won't you please let Furawa economically dominate the country or make me the new king?"
Jean: "Hummm, no."
Lilium: "Arggg, my masterful plan defeated!"
The show act like this is the best possible outcome, but its actually a terrible one. The prince still has the power to officially disband ACCA, he could just make a surprise announcement and that would throw the country into chaos. Furawa left, the rest of the country get miraculously saved by the discovery of new resource, but without that they would have been pretty screwed. It's not a stretch to say that Furawa would have been far stronger outside than inside since they could start charging a hefty sums to the other country. At worse it might have come to war. Plus the Furawa citizen are innocent in all this, but they could royally screwed over in all this, they foot the bill for the rest of the country and now there out with no compensation. In the real world there would be some massive legal battle since they might be able to claim that they deserve the lion share of the revenue of the new resource. The princess might still try to assassinate Jean and his sister (why did she even try that in the first place?), and why can just walk away from that like nothing happen? Her subordinate ended up killing themselves, that alone should have some pretty big repercussion (what are they going to tell the relative?), and she very well could have killed people for real.