2012, I think. He'll probably be released this summer. Then again, we've been thinking that for a while now!
He was good in the first half of the season. On that sort of form he displaced Marchisio from CM, so I don't see how you're under the impression Marchisio would start ahead of him in a 4-4-2 with proper wingers this time barring a "shift to the left" for him (Marchisio). Pirlo/Marchisio and Pirlo/Aquilani are just as flimsy as one another and won't work, anyway.
With Inler in the mix, even in a 4-3-3, Marchisio should struggle to get in. Ideally.