Chastened how? He's just made one of the most spectacular comebacks in history and scored a near-impossible victory in Belgium.
Certainly that is what the Allies will assume. And they know that the last thing they need is a truce giving him the chance to train up a new army. Their only sane course is to press on until his existing army is ground to powder.
Even if while being on Elba Nappy suddenly became a completely new man (who, however, just kicked the sh-t out of the Brits and Prussians but never mind), nobody would believe him.
I have very serious doubts that the Brits would capitulate just for the purpose of “saving” their army because Nappy was not going to start killing the POWs and those who matter (officers and generals) would be living comfortably in France. Defeat by Napoleon definitely would not come as a shock (OTL victory was considered almost a miracle), the Navy was there guarding the homeland and there were continental allies marching to deal with the Ogre.
As for the rest of the allies, they were ready to accept the casualties: this consideration did not stop them in 1813-14.
By the end of May, the total armed forces available to Napoleon had reached 198,000 with 66,000 more in depots training up but not yet ready for deployment. Approximately 100,000 had been deployed on the
main front (Armée du Nord).
The
immediately available coalition armies for the
main front numbered 742,000. Besides the Great Powers, most of the German states contributed.
So if Wellington’s Army of Flanders (93,000) is completely destroyed and Blucher is defeated suffering heavy losses of, say, 15-20,000 out of his 116,000 while Napoleon did not loss a single soldier (😂), the Allies still have the numeric odds much better than at Leipzig and they had 2 ready reserve armies, Russian and Prussian.
Additionally the allies had:
Swiss Army 37,000
Astro-Sardinian Army of Upper Italy 50,000
Austrian Army of Naples 23,000
Anglo-Sicilian Army
Prussian Reserve Army (3 corps)
Russian Reserve Army (2 army corps, grenadier division and Reserve Cavalry Corps)
Portuguese troops (12-14,000)
2 Spanish armies in a stage of mobilization
Danish and Hanseatic contingent
en.m.wikipedia.org
But if coalition falls apart, Prussia is #1 on Nappy’s list and if coalition falls apart due to the prussian “betrayal” Prussia is on its own. Not to mention that at that time the Prussians hated not just Nappy but the French in general and did not behave well in France so that they’d expect retribution in kind. Alexander is seemingly the least motivated except that he was dead set on destroying Nappy and on this he was backed up by the Russian public sentiment. Austria, just as Prussia, would expect retaliation in the case of Nappy’s victory.
Nappy was beaten in 1814 after a series of victories in 1813 and 1814 so how would it be different in 1815? The formula for victory was known and little changed. If anything, it was worse for Nappy because some of the marshals did not join him in 1815.
So to whom Nappy could appeal with some
believable proposals? And why would anybody believe these proposals?