On the positive side, since the Governor's race will be a blowout for Rendell, there may be less pressure to "get out the dead vote" in Philly. This would benefit Santorum, since Philly will go 90 to 10 against him. In order to win, he has to overcome the 200,000 vote advantage Casey would have coming out of Philly.
Why do you think it will be a blow-out for Rendell??
Everything I've seen says it is santorum going down, where swann is competitive.
Usually, the blues pick up pitt and philly and the reds take the rest. If Swann can flip pitt to red, Rendell will need one big graveyard vote out of philly to win.