Here's some more brainstorming on this important question: Will the violence continue? Probably, despite indications that it has subsided. The open source war is moving under its own momentum now (the participants in Paris are likely just dead tired and the collective thinking of the community was to rest). This means that Prime Minister Villepin's attempt to extend an olive branch will not restore any measure of lasting calm. Nor will the extra police since the guerrillas will continue to evade their patrols and overwhelm them when they engage. The only solution, egged on by many, will be the broad use of the military to restore order.
The use of the military, when taken, will shut down the insurgency for now. However, the presence of troops in the banlieue will be a source of provocation that will continue to fuel future efforts. Mass arrests will only make things worse. During the period of military enforced calm, France's open source guerrillas will radically improve their methods. The next time violence emerges, it won't be just cars that are torched. It will be the very infrastructure that France relies upon for modern life (via swarms much like we see today and new methods of cascading network failures). Given the efficacy of these techniques, the economic pain of this future conflict will be many times worse than the current one and will be shared by all of Europe. This conflict's long term impact on the future of French prosperity is hard to measure at this time, but it certainly is going to be severe.Finally, I suspect that at some point during this future conflict, France will come to rely upon empowered, local Islamic militias to maintain order in the banlieue. However, the ceding of authority to those militias will be exactly the type of autonomy that this was about in the first place. France will have fragmented.