A long lasting Civil War requires that the Commune has more support on the French mainland. This is due to, how likely outside European intervention is likely and breaking down this factor will leave us with Germany. But why do that, when, Alsac-Lorraine was under firm Prussian control and France dumbfounded? Maybe if Wilhelm I and Bismarck found it necessary to further leash the French people, rob them of foriegn support (if the Commune-ists achieve victory), and take there attention off their blistering hate towards Germany to avoid future conflict? It's as likely as it is unlikely. Perhaps much needed men to restore order are POW for a few more months, maybe surrendered arms, supplies, and all the rest are funneled to the commune. In conclusion, any form of sucess on the Commune's part lies with Prussia, which can either support them indirectly or not at all.