I wouldn't say the reason The X Factor gets 14 million is because of Cheryl. The show helped boost her profile, not the other way around. Cheryl has to thank the X Factor for where she is now because without the show, I bet she wouldn't enjoy half the success she has now. 14 million viewers don't tune in just to watch Cheryl walk down the podium to the judges panel. I believe the reason it's watched by so many people is because of the clever publicity that Cowell employs.
I'd be sad to see Dannii go. She is the only judge, along with Simon who gives regular constructive criticism in my opinion.