The radio graveyward is littered with the corpses of hosts who have tried to unseat Limbaugh.
O'Reilly has a very good television show (even though he has too many liberal guests). Whether he can duplicate that on radio is another matter. I predict that many stations that carry Rush live will carry O'Reilly on a delayed basis.
Rather have O'Reilly as an occassional alternative that some liberal host.
What may happen is O'Reilly may find himself sliding to a different time slot, probably morning. That might be bad for Howard Stern, because I like O'Reilly, but not enough to tune out Rush at lunch.
But my morning drive time might be split between Howard and Bill.