A likely coalition of Prussia (+ German minors), Austria-Hungary and Russia certainly would win any war in Europe.
France, UK and possibly Ottomans might be untouchable on the high seas, but the Ottomans in particular would be due a carve-up, and on land there wouldn't be that much the British could do to help the French. One might expect a longer, harder war in France itself, with no significant extra profit for the Prussians beyond what they historically got in 1871. The French would end up hating them worse than they did, and the efforts to control a defeated occupied France would be nightmarish for the Prussians.
Lord knows which way the newly formed Italy, with a certain debt to the French for it, would jump. Since the French would be the losing side, they just might sit the whole affair out.