Northern Italy just had it rough at the beginning of the 16th century, a playground between the Valois and the Habsburgs, with Milan being smack in the middle, the Kings of France attempting to press their claim to it, and in the end seeing the Holy Roman Emperor's son (and future King of Spain) installed in the Duchy of Milan when the Sforza dynasty when extinct.
But what if the Sforza dynasty had survived? It doesn't matter how, it's not too important. But rather than the French or Spanish ending up in possession of Milan, it remains independent under the Sforza dynasty. How does this affect European politics through the 16th century, and beyond?