From Bisping's blog:

Quick update on the potential Wanderlei Silva fight. Unfortunately thats not gonna happen. He's undergone facial surgery, so obviously won't be fighting in the near future. Rumours are he's actually out for the rest of the year.

So as of right now, Im still unaware of who I'll be facing at UFC 105. Obviously as stated before, when I know, you know.

Zak Woods elaborates:

Bisping's blog post at least confirms that the two camps were being approached about the potential fight. Currently it is rumored that UFC 105 will be headlined Michael Bisping in Manchester, England (Bisping lives in Manchester).

Without Wanderlei as an opponent Bisping may have to fight either the winner or loser of Maia vs. Marquardt in order for his bout to be a legit main event. Or the UFC could feature a title fight as the main event with Bisping fighting a different middleweight. Either the UFC middleweight or lightweight belts could be defended at that time.