With the capture of Prague and the reopening of supply lines, Elbe Armee's supply situation stabilizes, and attrition is brought down to a minimum as the Prussian army takes up winter quarters inside Dresden, Jungbunzlau and Prague. The Austrians remain out of sight and are presumably doing the same thing. No action is undertaken by either side.
Meanwhile, reports from the rest of the world arrive in Berlin. Marshal Browne, the commander of the Austrian army during the campaign of 1756, is incapacitated by disease and replaced by Prince Charles of Lorraine, Empress Maria Theresa's brother-in-law, who has no great record of victories, having been thoroughly defeated in multiple battles during the War of the Austrian Succession. In India, a British East India Company force under Robert Clive recaptures Calcutta from the forces of the Nawab of Bengal.
In addition to those come news of the declaration of war by the Holy Roman Empire against Prussia, bringing those German states under Austrian influence into the war. Even more worryingly, the Russian Empire signs the Treaty of Versailles, allying itself with France and Austria, on whose side it will likely soon join the war.
The most likely route of Russian advance in its very probably invasion attempt of the Kingdom of Prussia is through East Prussia and Pommerania. In the direct line of the Russians would be the two East Prussian fortress of Memel and Königsberg, the latter of which is a large fortress with a garrison of nearly 4,000 men, but which will likely not deter the Russian army for long. Beyond these is the Polish-Lithuanian Commonwealth, whose territory cuts off East Prussia from the rest of the Kingdom, which is technically neutral but, having lost the majority of its power over the previous century, now allows both sides to do as they please in its territory.
The fortress of Kolberg lies along the only major road along the Baltic coastline after Poland-Lithuania, with a garrison of 3,000 men. This fortress also houses the only Prussian field units in the area, an army of 23,000 men under Hans von Lehwaldt, which has been moved there from its forward position in Königsberg because it is far too small to threaten the Russian army. Finally, Stettin and Schwedt bar the way towards Brandenburg and the capital of Berlin.
The shortage of field units in the area means that any attempt to oppose the Russian army directly is likely doomed to failure, at least not without major reinforcements. However, the many fortresses in the way could slow down the Russian advance for a long time, possibly even until the following winter depending on when they choose to join the war, which might allow the Prussian army to set up proper defences. Additionally, the poor infrastructure in the region might allow light cavalry to harass Russian supply lines as they besiege the forts along the way.
Besides this route, the Russian might also choose to advance towards the south after taking Königsberg before moving west, allowing them to arrive much closer to Berlin, or go even further to link up with the Austrian army in Bohemia. Both these options will likely stretch Russian supply lines very far, however, as they will require extended operations inside the Polish-Lithuanian Commonwealth. Whether they attempt either of these options remains to be seen.