For anybody who is confused as to how the Dissolution actually came about, here is a bunch of information I couldn't fit in the description.

The emperor was assasinated with a crossbow. Since the balcony is about 4 or 5 stories high, it isn't unreasonable to suppose a well trained assassin could find a good vantage point or otherwise sneak into the crowd to shoot the Emperor with a high-powered one.

The Empire doesn't have a "constitution" like, say the US does. The constitution is more in line with a bunch of historical precendents, royal decrees traditions and the general authority of the standing monarch, a bit like the UK constitition. It's this history of legal ambiguity (as well as general discontent among the nobility) that allows the Council to declare the Dissolution later on, even after the codified constitution is in place. The absolutist constitution isn't in place until after Dunlain executes the Council, so it is, rather ironically, the formal establishment and marked increase in central authority that leads the whole system to collapse, when the vast majority of the nobility, deprived of their former authority, side with the Council a year later (note that they have a year to premeditate declaring independence, rather than just a day, as it might seem).

The Council of Lords, when it reformed after the assassination, wasn't a formal institution, it was a rogue assembly of the perpetrators of the civil war (Lotharingia, Bavaria, small lords of ex-HRE) as well as the Pope and the now Duke of Burgundy, as well as other malcontents. Those that weren't executed in the trial basically reconciled with the Emperor by siding with him in the civil war, even if they do sort of backstab him later on on Empire Day. (I'm looking at you, Anjou, Gelre and Upper Burgundy).

The Dissolution act is completely illegitimate (and certainly wasn't discrete, quite the opposite), it was the equivalent of an illegal trade union passing a federal law. However, the precedent of the move after the assassination of the victor mean that said members of the Council and others used it as an excuse to declare independence and establish themselves outside of the Seven Kingdoms , especially since the Council *was* a proper institution formed to assist Donell (who was quite incompetent) in his rule. The Seven Kingdoms are administrative units headed by artificial nobility (read: appointed), and so they don't have an army to defend themselves with during the Dissolution.

When the councillors were executed, their heirs are the ones who were still back in their respective kingdoms, and so assumed command and started the civil war in an attempt to weaken the Emperor. When they lost, their countries were occupied, but the soon-to-be councillors escaped and formed their little cabal elsewhere.

The assassination happens on the same day as the final battle, so there isn't really any time to consolidate authority in the occupied territories beyond suppressing partisans, so Vine is forced to assume command and evacuate the imperial retinues to Fynlund before the rest of the armies revolt in favour of their homeland duchies, which you have to remember are also independent now.

Basically, Vine is stuck in a situation where everything has gotten out of hand very quickly as a result of surprise, bad timing and unfortunate circumstances.

The Empire isn't completely dissolved because of all the threats surrounding the Empire, and because the Council aren't idiots, they decide that some semblance of central authority is needed, even if it can't directly influence them in any tangible way.

The Imperial Assembly, the restoration-era parliament, are the democratic (rather than aristocratic) replacement for Donell's Council, and they assume some (but not all) of the responsibilites Donell handed over to the Council originally, on the understanding that the Lord Protector views the assembly as legitimate and not overstepping their authority under the new constitution. He basically acts as a sort of non executive president-for-life, with powers of veto and dissolution.

Hopefully that clears everything up for you.