Just found another article for Heroes in Crisis with possible another hint at Ivy's fate:
SourceHarley Quinn, King said at his spotlight panel at San Diego Comic-Con, is around to support her lover, Poison Ivy, deal with a recent breakdown (and bid for global domination).
This doesn't bode well for her survival. Maybe Ivy left without Harley knowing or Harley got treatment after Ivy, but all this seems more of a stretch right now than Ivy being fridged...