I think Nixon would take Taft out on the first ballot at the convention, though Goldwater could play favorite son for Taft. Dont know if Rocky gets in with a surviving Taft. Nixon could play the moderate card or the conservative one, depending if Rockefeller intervenes.
I agree with pretty much everyone here, it's an easy victory for Nixon, though chances are he may choose a different running mate (which in itself could be no bad thing).
From what I know of Taft, he was honorable but stubbern and was a firm Isolationist write up until his death, so all Nixon needs to do is state his foreign polecy credencials and experience in the Eisenhower administration, 2 things Taft won't be able to do. If Nixon gets vocal support from Eisenhower earlier than IOTL (which I imagine could be quite likely, as I can't see Ike letting Taft have the nomination), then that alone could swing the election Nixon's way.
I think if Rockefeller ran you'd have all the wings of the GOP represented (sort of), Taft for the conservatives, Rockefeller for the left and Nixon in the middle.
If Taft somehow wins the nomination it'll be a Landslide (or at least a convincing victory) for JFK come November, as Taft can't credibly run for Ike's third term like Nixon could.
Furthermore, Taft would be lucky to get either a grudging presidencial endorsement, or Ike's voat in the election-I just can't see Eisenhower supporting Taft anymore than strictly necessary.