What if Saruman had repented at Orthanc ?

[Gordis]

WOW, Legate, what a great post! I like "what if's" so much and your scenario is excellent.

In your answer the changes to the history are minor. But you see, IMO, you displace one straw and the whole pile may collapse. For instance:

At night, a winged Nazgul flies to Orthanc [...] Gandalf is shocked, shouting the War has come and calling Shadowfax. He instructs everybody to go wherever they can and rides to Minas Tirith. [...]Merry and Pippin secretly make a plot - two silly hobbit heads work better than just one - to get into the Rohanian army.

Now Gandalf leaves alone, Pippin is left with Merry. They would try to ride with the Rohirrim, naturally sticking together. But Eowyn can carry only one hobbit on her horse. So what? Would both hobbits remain behind? Or would they find another horse to ride together?
Anyway, there would be no hobbit close enough to help Eowyn at the Pelennor. Not only would she likely get a free ride to the houses of Lamentation, but the Witch-King would remain alive and well. And here the victory of Pelennor becomes uncertain, Saruman or no Saruman.

I am not saying that all this will necessarily happen. Maybe something else will go wrong. There are so many what if's...