Poland was already reoccupied by Prussia and Russia by 1813. IMO, anything east of the Elbe is a foregone conclusion even if Napoleon wins at the Battle Of Nations.
But if Nappy wins the battle, he'll have a lot to gain. The Coalition will be dismantled and its member countries might give up on trying to defeat Napoleon now that he's earned a reputation for invincibility. To the west, the british could end up finding a negotiated peace better than keeping on -- Iberia was already in the british camp. As for France, Napoleon could use such a period of peace and a longer life in control of the country to better consolidate his position and prompt the first empire's survival. That is, if an opportunity for more conquest doesn't show up, as we know how much of a power glutton he was.
Firstly, the Continental Allies will not make peace.
Why should they when they have seen Bonaparte repeatedly defeated in person
They will see this setback just as they did Lutzen and Bautzen,
the struggles of a doomed beast caught in the net of it's own arrogance.
They
might agree to another
temporary armistice
but only because they know they are in a position to make better use of any delay than Bonaparte.
Secondly, Britain will not make peace.
They did not after Austerlitz or Jena or Wagram.
Why should they now when their Naval stranglehold is a tight as ever
and they themselves have driven Bonaparte out Spain humiliating Marshal after Marshal?
Thirdly, Napoleon cannot afford to make peace that leaves him only the ruler of France while still at war with Britain at sea and in Spain with (potentially) hostile nations across the Rhine.
France is bankrupt and cannot rebuild under blockade.
His plans for the Navy are pure fantasy
- building the ships
may be possible, creating a fighting navy is not in any practical timescale.
As to the army, there was already a man power crisis.
Conscripts for 1814 have already been called up and of them many had taken to the hills rather than serve.
Smuggling and other evasions are rife in the civilian population.
His only support in among the existing army, and even there was shakier than he liked.
It was not just personal feeling that lead him to say iOTL "Peace? No peace till Munich is in Flames!"
Fourthly, Bonaparte's personality would never accept any limits to his ambition.
He was after all refusing the offers of France's "natural" borders as late as 1814
with Allied armies already marching into France.
It genuinely was all or nothing for him, both practically and psychologically
So even if he wins at Leizig, he has to go forward again
Brer Rabbit, grabbing at the tar baby.