The long-term effect depends on how long the resistance movement can sustain the campaign. If it is just sporadic actions by some individuals or small isolated groups, the occupiers would quickly put them down.
Success factory for such an insurgency would be
- Reliable support by local civilian population
- Autonomous cells loosely coordinated by civilian leadership
- Efficient intelligence network to detect infiltration and traitors
- Financial and logistical support from German areas outside French control
- Professional experience in guerilla and commando warfare
Pretty much what all insurgencies need. The last point should not be a problem given all the WW1 veterans organized in Freikorps.
I am not quite sure why exactly the insurgency didn't happen to that extent. There were enough Freikorps, but either they didn't have the resources to fight such a guerilla war, or their primary goal was the downfall of the Weimar Republic, hoping to deal with the French after that. Also they were enganged in operations against communists and Polish insurgencies in Silesia.