Series creator David Shore said this...
“It’s going to be a while unfortunately. We love her but it is going to be a while. It’s going to be this season, but well into this season, She called us up and said she wanted to do [The Change Up]. And it just so happened that what we had worked out storyline-wise allowed her a couple of extra episodes [off]. So that movie just filled in the gap. There were no further adjustments to her schedule as a result of that.”
Olivia will make an appearance on the season premiere, but that's it for a while.
Sad day :(