In any event, when it became clear that Nixon was going to go down, Republican Party leaders looked aghast at the prospect of facing the voters with Agnew as the face of the Republican Party. They found a way out, by having the Justice Department indict Agnew on bribery charges. He was gone in a flash, and thus they were able, with Democratic Congressional support, to put a safe, uncontroversial place-holder into the vice president's office, Gerald Ford, who was at the time the minority leader of the House. It made a certain sense given that had Republicans been in control of the House, Ford would have been the next in line for the presidency.
If impeachment hearings made it clear that Bush's days in office were numbered, as I believe would certainly be the case, Republicans would be at least as concerned about being stuck with Cheney as their party leader heading into 2008 as their forebears were of having Agnew in that position.