Well it wasn't just Austria-Hungary. It was all of the southern German States ,ie Bavaria, Wurttemberg, and Saxony. If the war go's better for France in the first month, then Austria and the South German States would be much more likely to intervene. However, if Austria gets involved with the war and the war still gos bad then both France and Austria would be screwed over. After all, this would be the 3rd war in a row that Austria lost in 10-11 years. A revolt/revolution might brake out in Vienna as well as Paris.