The PC's loss would probably be blamed on Harris being too right-wing for most Ontarians, so I think the PCs would probably choose a more centrist leader. Beyond Ernie Eves, the other choices that come to mind are Dianne Cunningham (who lost the 1990 leadership race to Harris), Elizabeth Witmer, and maybe even Hugh Segal.
I agree with RB, though, that the Liberals would likely be defeated around 2003.