Had French forces crossed the border the Wehrmacht had orders to immediately withdraw from the Rhineland offering no resistance.
Hitler’s confidence would have been dealt a blow to say the least, and French confidence would have been boosted enormously.
Perfectly true. The real problem is to get the French government to march into the Rhineland in the first place. But this is precisely the POD the original post had already taken for granted. If even Hitler acknowledges that his forces are vastly inferior, and orders a retreat, then the French army and government cannot help but succeed.
If Hitler does not give the order to retreat, the tiny German force in the Rhineland has the alternative of either surrendering or getting wiped out.
The French now have gained two huge advantages:
1. They have occupied the Ruhr district, as a part of the Rhineland. This is by far the biggest and most important industrial area in Germany. Germany's prospect for gaining even military parity with the French are not good, and the prospect for beating a coalition of France and Britain, not to mention other countries, have become utopian.
2. They have humbled a dictator whose unspoken motto is "might makes right" and who, so far, has impressed quite a number of people inside and outside Germany. If people find out that Hitler cannot deliver the "might", most or all of his prestige will vanish overnight. Every German at the time either remembered the hardships of World War One very well, or knew many people who remembered them. If Hitler failed this early in his career, they will rightly fear another war as a total disaster.
France's allies on the other hand, will regain confidence in France. Belgium will not renounce its military convention with France in 1936.
If a French government has decided on re-occupying the Rhineland (as is stated in the OP), they cannot help but be successful. Once they, and the French public, realize that they have been successful, there is absolutely no reason why the occupation cannot remain in place for many years, let's say until Germany becomes a democracy again. With the Ruhr district in French hands, the Germans cannot defeat the French.
There still may be other big wars in the future, but definitely no World War Two as we know it.