Talleyrand suddenly dies before the Congress of Vienna and France is left completely out of the negotiations. Besides losing all their territorial gains as in OTL, France is forced to pay unreasonable reparations to the other Great Powers ITTL. Louis XVIII is restored, and supports a harsher purge against anyone who is thought to have supported Napoleon.
This (except Talleyrand dying) is essentially what happened in 1815 after the Hundred Days. The second settlement was significantly harsher than that of 1814, and there was a White Terror.