You could see this
thread of five years ago that I shamelessly take his images, that are really good for this question.
Ok, if we have a Partial war, then Paraguay at least could don´t lose as bad or end in a Tie, the principal Problem of the Triple Alliance War, was that Paraguay Causis Belli was bad, really his motives to start the war immediately put them against Brasil and Argentina.
A good form to stop this is that Paraguay and Argentina Fight a War before. Why you ask? because Argentina could be defeat by Paraguay Alone, Paraguay was more stable, secure and with better standing
Army than Argentina in the period previous to the triple alliance war,after the country was barely a country.
Country Army Navy Artillery(source)
Paraguay 60,000 27 ships 400 cannons
Alliance (Total) 26,000 47 ships 239 cannons
Argentina 8,500 5 ships –
Brazil 16,000 42 ships 239 cannons
Uruguay 2,000 – –
So Paraguay declare a war to "Liberate" o "reunited" the guarani population of the Argentinean Yoke, Paraguay considered itself as mestizo population were all his population is half Spanish half guarani, how true is this affirmation is another basket, or Argentina close the Paraguay River to the Paraguayan Commerce, or Argentina Taxes more all the commerce coming from Paraguay(the same causis belli that the War of the Pacific). o Paraguay at the lack of better options invade Argentina and Take the Actual regions of
Misiones y
Corrientes plus they don´t lose the territory of the Actual
Formosa Province of Argentina, there is little doubt that Argentina alone against Paraguay lose the war, if someone have other sources That say otherwise please feel free to respond.
As this war don´t involve Brasil, and historically Brasil an Argentina in the XIX century are in complete opposition, Brasil don´t intervene and could even support Paraguay effort´s as they could use Paraguayans as buffer state between then and Argentina.
so we have Paraguay that look more similar to his "claimed frontier"
Next we have the Brasil-Paraguayan War. Again Paraguay have a lot of advantage against Brasil, the sames as against Argentina, plus a bigger Territory, and a more developed Industrial base, in the XIX c. Paraguay was the more industrialized country in South America, they have a native, munition, weapons, metallurgy industry, plus a telegraph in his most important lands. that his bigger neighbor's lacked.(
source in Spanish)
plus with his new territory they could more easily intervene in Uruguay.
so how the Brazilian-Paraguayan war goes?.
this i a question that i don´t know enough about Brazilian forces to respond could It be the same that in OTL, Could it be a stalemate that end with Paraguay maintain all his gains from Argentina, could it end better to Paraguay and Uruguay with Brasil losing Rio Grande do Sul and this territory being incorporate to Uruguay, and Paraguayan gains in Mato Grosso do sul, my personal favorite but i´m not sure how make it happen, Uruguay was a mess before 1904 because the
Guerra grande(great war) that officially ended in 1852, but was the cause of the Triple alliance War.
So in case of a Tie we end with a Paraguay that look like this:
or they could don´t fight a war and end being a industrial powerhouse in the middle of south america, both option are valid