They're not in the new DCU!... At least for the moment.
The news is just in, via Zechs via the BleedingCool.com, where it has been stated what the fate of Cass, Steph and Donna is in the DCnU.
And the answer is... they're "benched".
Well, being in limbo is better than being dead, I guess. Still annoyed though.
Information from here, from the mouth of DC Senior VP Sales, Bob Wayne,
Fanart to ease the pain,
The Blackbat by ~r4r3truffle on deviantART