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Say that forces loyal to Sigismund III are defeated in battle of Guzów. Sigismund is stubborn, keeps fighting even after the rebels are trying to force him to accept their demands (abolishing king's right to nominate government officials and ban foreigners from having any influence at court) in exchange of being kept on a Polish throne. Sigismund still refuses and Warsaw is captured by rebels. Sigismund is tried and beheaded as a first European monarch. His wife and child (only son Władysław, because his brothers aren't born) escape to Vienna, under the custody of Emperor (Władysław can end up as an earlier Eugene of Savoy in imperial service). In Warsaw, new king isn't going to be chosen. Instead rebels are upset with monarchy and make "Council of a Commonwealth" (a body consisting 12 envoys, chosen by a House of Envoys and 12 senators, chosen by Senate) a collective head of state. Sejm is right now only power in the state. Would such situation last long? There is no more king to blame for state's failures. There is no more king to be accused of tyranny. The new government would try to make peace with Charles IX of Sweden because Sigismund (and his supporters) are his common enemy. On the other hand, Polish diet wasn't among the most effective in Europe and without king to unite noblemen the tensions between lesser nobility and magnates would rise to levels never seen before. The rebels wanted also to get rid of Jesuits, which would conflict them with Catholic Church. This would create an unrest from actions of a new government. Possible it'd mean the rise of support for return of Władysław. But the military and a prominent rebels would be against it, fearing Władysław's revenge. An hero of a civil war, Mikołaj Zebrzydowski could try to pull a Cromwell and seize power for himself in military coup creating Protectorate-like military dictatorship. The Polish intervention in Russia would not happen with such a state of internal affairs. It means that Vassili IV is going to sit on the throne longer. @Jan Olbracht