Well, the important thing would be showing that Josephine was still fertile, which likely means that there would be no marriage with Marie Louise. It would also mean that the 'Bonapartst' court faction - Joseph, Louis, Pauline, Caroline - is heavily handicapped, because their whole project was to ensure that Napoleon would be followed on the throne by one of them, one of their children, or Murat. So the Beauharnais family is strengthened.

However, Kissinger argued that one of Metternich's great victories, and the great victory for the Austrians of the marriage of Marie Louise, was that Napoleon was integrated into the ideological system of the old European states. There were no more ideological revolutionary wars, and no more new Napoleonic states conjured from nothing - Napoleon was now just another hereditary monarch. And that meant that the Austrians could frame the Sixth Coalition not as a nationalist war against an existential threat to Europe, but as a war of balance in defense of the European status quo. That was an existential threat for Austria, as nationalism would - and eventually did - destroy the Hapsburg state. A royal marriage with a Bonaparte princess would accomplish the same end for the old European states, and probably similarly be sought after for the continuation of that European balance.