The Sforza dynasty continuing probably means it ends up like Tuscany, as the Habsburgs support the Sforza as a bulwark against French influence (the French are likely to cite the Orleans claim if and when they invade Milan, regardless of the Sforza dynasty surviving), but if and when the dynasty dies out it is likely to be claimed by the Emperor regardless, much as happened to Mantua.
Beyond that? Well it all depends. Historically the Savoy savored Milan- if the Sforza go extinct, there might be a dynastic claim which the Savoy could use, or vice versa. I would think that, post Napoleon, one might potentially see an Italian confederation or perhaps a Lombard/Padanian state emerge as a bulwark against France... it really depends on how the intervening centuries go.