There are many factors that will influence whether the transfer occurs in the next month or two. It is clear that Wenger would understandably like to keep his prize asset at the club but he knows that keeping an unhappy player in the squad could be detrimental. Cesc owes a great deal to Wenger and Arsenal and it is unlikely he would hold the club to ransom.
Another factor is whether Barcelona can (and want to) match the asking price set by the Gunners believed to be at about 40 million. Things haven't been as rosy financially as they have been on the pitch for the Catalans who have gone against past tradition in getting a shirt sponsor for the first time in history due to fiscal constraints. Does Wenger have a replacement in mind for the skipper? Can any Barcelona player be realistically used in a part exchange deal?
I think the chances of a summer transfer to Barcelona for Fabregas are about 50%. Regardless of what happens, it is important that decisions are made early so that we have time to not only replace any players leaving but improve the football squad.