So, as it says on the tin, what might have changed had Sigismund Francis, Archduke of Austria, and ruler of Tyrol had lived passed his death in 1665, and sired a son with his wife Hedwig? I assume this would mean that Tyrol remains separated from the mainline Austrian inheritance for a period of time, and that there might be a candidate for imperial election should something happen to the mainline further on down the line.
Other than that what could happen?