Tolkien believed that if there was not going to be a Scouring of the Shire scene, there was "no good reason for making [Saruman] die."
He wrote that the Saruman plot thread should instead be "tidied up" by having Gandalf tell Treebeard to keep Saruman in captivity. He even provided some example dialogue: "Since you will not come out and aid us, here in Orthanc you shall stay till you rot, Saruman. Let the Ents look to it!" Though the wording differed, Gandalf expressed that exact sentiment in the theatrical cut of Jackson's film.
Exactly what happened in Jackson's theatrical cut.
Didn't need an article that long.