Just read Ayu's latest instagram post and it seems like he's not leaving the troupe permanently but that she won't be using a live band for the hall portion of her tour. (although when she said "band-less" maybe she was just referring to Yocchan)
Also, as pointed out above, he said "last time
this year" So hopefully it's a temporary parting due to her lack of a band for the hall portion of the tour
It also might be because he's got other activities outside of her tours and her tour dates are clashing with his other commitments.