Tend to agree with Armor and Ron here.
In any our set up, he'd get multiple opportunities to be the most advanced of midfielders, in any case, during the course of the game. (Especially, if Wilshere is playing)
Also, I think, Wenger has given up hope on Diaby. I remember him talking about how Diaby had to earn a new deal, last season. And Diaby, though for no fault of his own, has clearly not earned it. I think, this could be his last year in the current contract and most probably, he'd run it and move back to France on a free transfer.