If you want to separate the French, German, and Italian portions, after all have been part of Switzerland is a ht tough because a lot of the French parts were added after the Napoleonic wars. Really, anything after that, I'm not sure Switzerland would become separated because after 1815 the Swiss are officially neutral. Perhaps the best point to do it after that would probably be during the 1860's with Italy and Germany conjoining. But at that point tbe Swiss were a pretty distinct portion of Europe and I don't think integration would come easy.
Even simpler actually. While certainly part of the Francophone territories were acquired at Vienna (namely those which had been part of the Prince-Bishopric of Basel, loosely associated with the Old Swiss Confederacy at various times) , the area of the canton of Vaud had been acquired in 1536 in a war with Savoy and was predominately French speaking as well, along with Neuchatel and parts of Fribourg and the Valais.
Now, the Old Swiss Confederacy was more of a permanent alliance of otherwise independent states than a unified body, but it had a unified foreign policy (for the most part) and was recognised as independent from the Holy Roman Empire following Westphalia so I think this counts enough. In essence we can dismember it during the Revolutionary Wars:
1. The establishment of the Lémanic Republic is followed, as OTL, by a French invasion and establishment of the Helvetic Republic, rather than being made a canton of the new republic Léman is instead split out as a sister republic (including more of Fribourg than OTL), later being annexed into France at the same time as the Rauracian Republic (formed from the Prince-Bishopric of Basel). History progresses roughly as OTL, with the Valais being annexed to France in 1802, but the Ticino is detached and annexed to the Cisalpine Republic at the same time as the Valtellina. This leaves a rump Switzerland that is near-exclusively Germanic (Neuchatel having, as OTL, being granted to a minor general) save for the Romansch and possibly a small French minority in Fribourg. Switzerland gets forced into the Confederation of the Rhine, and then Napoleon dies in 1812. In the resultant peace treaty France agrees on a minimal restoration of the old order- the Kingdom of Italy (including the Ticino) under Eugene de Beauharnais remains but the Papal States are restored to Latium, Sardinia is also restored (plus Genoa but minus Nice and Savoy) and Tuscany+Lucca+Parma is made a Habsburg puppet state, Austria also annexing the Istrian territories. Murat retains Naples by dint of not doing anything stupid, the pre-war situation is restored for Spain, the Confederation of the Rhine largely dismantled and France is able to retain all annexed territories west of the Rhine, including the Swiss annexations. Rump Switzerland is bundled into a new Germanic Confederation and eventually ends up either following the path of OTL Austria or being incorporated into an eventual German Union.