In practice, it ought to be conceded that every part of this plan was high risk, given that they all fail – but while the complete failure of Saruman’s plan was necessary for our heroes’ hail-mary pass to defeat the larger threat of Sauron, as we’ll see, the failure of any part would doom Saruman. The only scenario in which Saruman survives, much less wins, is one in which he both defeats Rohan and captures the One Ring (it can hardly do Saruman much good if Uglúk returns with the Ring to a defeated or besieged Isengard, or if Saruman has the ring but no army), and that the ring does everything Saruman hopes it will do.