Jill Zarin made her Real Housewives of New York exit after last season. Although she isn't part of the show anymore, she's still very much remembered and whenever she talks to press, the show and its current cast members seem to always come up.
As for what it would take for her to consider returning, Jill told Rumorfix, "A lot of money." She adds, "I don't know. I'm sort of kidding. I never did the show for money so it wouldn't really be a lot of money to bring me back." Jill was fired and while many think that is reason enough that she'd never be asked back, the truth of the matter is that ratings have dropped drastically since she left.
Either way, the producers at Bravo would likely not want to have her back because if anything, it would look as if they didn't know what they were doing. Having to bring back an axed cast member would more or less be them admitting fault.
Jill Zarin maintains a relationship with Countess LuAnn who she plays tennis with regularly. Shockingly enough, she's even in communication with her former RHONY enemy, Ramona Singer!