If before the war of Crimea, not necessarily an Imperial Austrian fall will necessary favour an Italian reunification but probably obstacle it, as without Austria there will not be need for Napoleon III to create a unified Italian cushion state - and Nappy in truth wasn't in favour of a full unification but only of the North of Italy. Naturally, after 1861 but still prior of 1866 Italy had all to gain from an Austrian collapse and France all to lose, because with the eventuality of a disgraced Austria the idea of the Great Germany could take life and Bismarck will surely concede to Italy the irredent territories in exchange of an anti-France alliance (above all for Rome).
In substance: until the mid 1850, an Austrian fall IMO will not bring advantage to the Italian unification, more later yes.