An alliance between France and the NCG (aka Prussia and assorted midgets) is not ASBish at all, provided that Louis Napoleon is convinced that after Mars-la-Tour the military situation is not recoverable, and decides to cut his losses. A request for a ceasefire is granted, and military operations end during the last decade of August. LN moves to Paris to put a stop to the unrest in Paris, and keep the regime alive (and the empresson a short leash). The government of Cousin-Montalban (who replaced Ollivier after the vote of noconfidence on 9 August) will have to be dismissed, since the only reasonable way out is to form a government of national unity backing the regime and the attempt to signe a peace treaty with Prussia and friends. The problem is who is going to head this government of national unity: Ollivier is completely discredited, the emperor cannot draft MacMahon who is needed in Chalons at the head of the last standing army of France, it would be politically impossible to choose anyone from the Left or from the Mamelukes: I'd put my money on gen. Trochu, who had not been tainted by the recent defeats and could read the writing on the wall, but I'm not completely sanguine on this (if someone can suggest a credible candidate I'd be very happy). Peace talks start soon after (possibly in Switzerland or in Belgium: Bismarck wants this peace treaty too, so he should be willing to save the emperor's face). I'll go out on a limb, and assume that Prince Bonaparte (Plon-Plon) will lead the French negotiating team: it is a kind of stretch, since in the 1860s relations between LN and his cousin were not the best; OTOH Plon-Plon and Trochu were the strongest voices to oppose the mad ride to Sedan, and it's not that LN has a lot of options. My position has always been that in such a scenario Bismarck would not go for the jugular, and be satisfied with a demilitarization of the Rhenish border on the French side plus the demolition of the fortresses of Metz and Strasbourg and a reasonable amount of reparations (B. does not want a long war and even less a republic in France). The peace treaty should therefore be signed in September, and LN can concentrate on how to save the regime and the inheritance of his son. Some empty words about future eternal amity between the NCG and Imperial France will certainly be added to the peace treaty.
The formal alliance treaty will not be signed immediately, but if the regime survives the first bumpy year or two it may look like the best solution to the sick French emperor, and might come to pass before 1875. One might wonder why Bismarck would choose France over Austria-Hungary: economically there would be better synergies between the NCG and France, such a treaty would do wonder to reduce the worries of the southern German states that a revanchist France might raise in the future, more simply a weakened France may look a much better partner than the A-H empire (where in any case B. would still enjoy good relations with the Hungarian half). If B. manages to bring home this coup and at the same time keeps his traditional good relations with Russia, Prussian dominance in continental Europe would be almost certainly assured
