Reportedly, Sato will leave in the end of February, while Mukaida's graduation will be in the end of March, but more detailed graduation dates for both girls will be announced later date.
After the performance, Sato updated her Google+, and made a comment toward her fans, "I will continue doing my best as my usual self while leaving every single day in my memories? Please support me until the end!"
Source & Image: natalie
Thanks to Josh for the tip!