[The Squatter of Amon Rûdh]

Of course if Saruman falls on the fellowship at the Gap, and manages to get all of them back to Isengard as captives, Gandalf isn't free to rouse Theoden; Aragorn can't take the Paths of the Dead and Minas Tirith falls (not to mention that Merry and Pippin can't turn up in Fangorn just at the right time to spark off the rising of the Ents). Assuming that Saruman would be stupid enough to take up the Ring and challenge Sauron immediately (I think that he would; he seemed pretty confident of his power) the main army of Mordor then turns up at Isengard and pulls it to bits. Result: catastrophe; the rule of Sauron and Saruman ends up worse off than he does in the real story.