On March 15, 1756 "the Conference" (cabinet of the ministers) of Empress I formulated the the purposes and goals of a planned war against Prussia (at that time Franco-Russian-Austrian alliance did not, yet exist).
The main goal was to cripple Prussia of Frederic II to such a degree that will prevent its further strengthening and eliminate it as a potential danger to the Russian Empire. For this purpose the Russian-Austrian alliance has to be created and France (at that time Prussia's supporter) kept neutral while Poland should be diplomatically prepared to the passage of the Russian troops through its territory.
Post-war arrangements had been planned as following:
(a) Poland is getting the Royal Prussia
(b) Austria is getting Silesia
(c) Russia is getting from Poland Courland (which, while being formally Polish vassal already was more or less controlled by Russia) and some vaguely defined "troublesome" territories capable to support the trade route between the Baltic and Black Seas (Western Ukraine?).
In OTL, even with many things going not according to the plans, the initially set goals could be achieved: at least after Kunersdorg the allies came dangerously close to them. The East Prussia was under Russian occupation, Prussian army suffered very serious losses and energetic pursuit of the achieved advantages could result in the Allied occupation of Berlin by a major force which did not happen due to the "
Miracle of the House of Brandenburg." (not to be confused with the "2nd miracle"): due to the disagreements about supplies between Saltykov and Daun (and the fact that both of them had been on rather cautious side) the joined allied offensive did not happen.
Now, what if the (known in advance) supply problems had been resolved earlier? Russian troops had supply bases on the PLC territory which means that at least some of them had to be brought by land across the whole Commonwealth. Only closer to the end of a war the measures had been taken to provide an optional route by the Baltic Sea, hence the siege of Kolberg in Pomerania. However, this could be done on the earlier stage of a war eliminating at least some of the supply problems (and the sources of disagreements between the allied commanders). More aggressive generals on the top would not hurt either.
Anyway, let's assume that "idiot's dream came true" and Fritz is forced to ask for peace in the summer of 1760 (the Austrians are occupying at least a part of the Lower Silesia but Battle of
Liegnitz did not happen). The Allies are in a possession of Berlin and Pomerania (and perhaps of at least part of the Upper Silesia as well). OTOH, the Prussians are still holding Saxony.
Scenario #1: Everything happens almost according to Elizabeth's laundry list. Russian troops are evacuating Pomerania, etc. Royal Prussia goes to the PLC, Austria is getting back lower Silesia. Russia is getting Courland and most of the PLC territories which ended up in the Austrian hands after the 1st Partition (Galicia).
Scenario #2: Like #1 but Prussia is getting Saxony. In this case the Royal Prussia is returned to the PLC as a personal domain of the Saxon dynasty.
Questions:
1. Prussia. How would this change the further developments in the Eastern Europe and how much the loss of Eastern Prussia and Lower Silesia is going to cripple the further growth of Prussia? How acquisition of Saxony would change the situation?
2. The PLC. How would acquisition of the Royal Prussia (and loss of the Western Ukraine) impact the PLC in the terms of its future ability to survive as an independent state?
3. Hapsburgs. How things would be different for the Hapsburgs?
4. Russia. Impact of the earlier and different "Polish acquisition" on Russian Empire? I'd assume that instead of a desired peace and transit trade there would be an earlier war with the Ottomans.