Italy would be trying to get the territories promised to it as a part of the Treaty of London. The German minority was tiny and dispersed throughout the country, so I'm not to sure what Hitler's cassus belli would be. They would defeat Yugoslavia quickly, especially if they have help from Hungary and Ustashe. But the partisan problem would still be there. France, UK, and Poland would all be alarmed and would accelerate their military re-armament. After seeing Yugoslavia get blitzed all 3 countries would likely put their armies into permament mobilization. I'm assuming no Molotov-Ribbentrop Pact, so if Poland goes up against Germany it will be able to try the Romanian bridgehead strategy. France and the UK would probably start carpet bombing German cities from day one of the German invasion of Poland. (It's likely that Germany would have done that to some Yugoslavian cities, so the Allies will have no hesitate about doing that to German cities.) Belgium will probably be more willing to cooperate with the Allies. With the extra preparation time, seeing more of Germany's blitzkrieg tactics, more German losses in Yugoslavia, and German troops held up occupying Yugoslavia, it is likely that France does not fall.