Kara is the easiest judge to lose because her contract is year to year. She has yet to be renewed for Season Ten. (At least no announcement has been made.)
They could drop Randy, but they would probably still have to pay out the rest of his multi-year contract. Still, that's chump change compared to what they are saving this year by not having to pay Simon Cowell his $10 mil / year fee. Buying off Randy would be money well spent, from my point of view.
To misquote Shakespeare:
"The first thing we do is kill off the judges."