Interesting.
Considering the French mindset - far from ASB.
It is not that far from OTL - the newly formed IIIrd Republic kept on forming new armies after the Imperial Army had surrendered at Sedan and Metz. Which IIRC baffled the Germans ...
I'm fairly sure that the Northgermanfederation + friends would have financial problems in keeping a large army in the field, thus leading to looting imposing contribiutions (see Leipzig 1866) and general heavy handedness towards the population, thus fueling resistance.
However, the difference is that unlike Napoleon in Spain, the Northgermanfederation + friends did not have ambitions to subdue the whole country. Hence I wonder how long would it take Bismarck to beat into Wilhelm's skull that "treaties are overrated" and the Prussians retreat to a line of their choosing and "dig in" there.