Creative thinking but I'm guessing that IF Ricky were put on the Supreme Court, Rendell would nominate somebody other than Casey unless Casey really wanted it.  That somebody would likely have to make the "I won't run" pledge to allow Rendell to nominate somebody without being hassled.  Casey would likely still be the nominee in 2006 b/c he's done too good a job in getting his campaign in order at this point. 

The 2006 GOP primary would then become a blood bath.  My guess is that any one of these candidates instantly become top teir: Ridge, Toomey, Hart, Pippy and any other number of people who might run.  My guess would be that Hart declines, looking to run for gov in 2010.  Pippy might do the same but look to run for another office in 2010.  Ridge has made complaints about gov't pay in the past so if he ran it would be a big surprise to me.  I think Toomey, like Hart has his eyes set on 2010.  He can either run for governor (which I speculated on back in 2002 after his win then, mentioning the prime reason he ran in 2004 was to improve his profile... I don't think he really expected to do as well as he did and I know a number of LV GOPers of the same mindset).  My guess is that Toomey runs for governor/senator in 2010 and Hart runs for the other office.  This of course assumes Arlen is done.

As far as the SC nominee goes, the administration did a good job of picking a nominee with little public profile so I'll assume the same will happen again. 

And for the record, I think Santorum will lose by the same margin Fisher lost by to Rendell in 2002.  He's turning out to be a consultant's nightmare of a candidate.