Consider that they wait until SC announcing the disbandment of Kalafina to post the message, I feel like what they wait is the moment when Keiko and Hikaru are completely un-tied from SC. So I think that no one would mention Wakana who's still under SC, whether they still keep their connection or not. And Wakana would do the same thing. It might put Wakana in an awkward situation in her workplace if they do that. (I think it's just a common thing in all workplaces around the world when some employees left their workplaces in a bad term.)
I guess that when Kajiura left SC, she didn't intend to see the end of Kalafina after her left, but expect that the band will just continue under another producer? (They already had their own Harmony, splitted from FJC.) But after the members keep leaving SC, disbandment becomes the most reasonable thing SC should do IMO. Probably, what she might not expect the most are Keiko's and Hikaru's leaving, which leads to the disbandment.