As in the title what would be the effects of the entire Prussian royal family dying off during the war of 1806-1807? Some die in battle, other die in accidents, couple are murdered by French soldiers, and finally what's remained of them dies of some or another ilness in winter?
Anyway, by the time of otl battle of Eylau, all of them are gone.
Anyway, by the time of otl battle of Eylau, all of them are gone.