The peace terms would depend on a number of factors. Is France acting alone, or with allies? If alone she would probably annex Luxembourg, baulk at the idea of further territorial aggrandisement (which would bring a large number of Germans into the Empire) and settle for a large war indemnity. The rise of nationalism in Europe after the Napoleonic Wars would leave France disinclined to have a larger German speaking minority, already enough in Alsace and Lorraine, and mindful of not upsetting the continents two super-powers would probably leave it at that. Should Bavaria fight on the side of Prussia then the Palatinate might just be up for grabs, a strong war party in France might demand everything between the Rhine and the Moselle rivers erecting border posts just south of Koblenz, something that the emperor might just chance his arm on. I can't see that either Great Britain or Russia would look favourably on France taking all the left bank of the Rhine up to the Netherlands. Of course, if France acts with allies then this becomes a whole different ball-game. Allied with either a disgruntled Austria following her defeat in 1866, or Austria and the south German states, the stakes become higher. Expel Prussia from the Rhine, reversing the decisions of the Conference of Vienna? Allow Austria to regain Silesia, Saxony to regain its former territories, reconstitute Hannover, there are a huge amount of possibilities. But, and this is a huge but, France would have to be wary of upsetting Great Britain and Russia, two countries that fought long and hard against Republican and Imperial France to stop Gallic hegemony in Europe.