He's all over the local newscasts here in PA. I think he's trying to send a signal that despite his illness and treatments, he can be an active and effective Senator. I don't think there's any chance that he would resign and allow Rendell to appoint a Democrat to fill his seat. Like Strom Thurmond, even if they have to prop him up in a chair, he's not going anywhere.
They're probably going to have to prop him up in a chair because I'm sure that he's determined to hang on long enough to influence the Supreme Court nomination to replace Rehnquist.