One of the central arguments in my recent paper on Dating the Crucial Sources in Early Christianity (Handout; Blog Series on Dating) was that Mark's focus on the temple, in which prophecies of its destruction, alongside a narrative climax that stresses its connection with Jesus' death, makes best sense in a post-70, post-destruction context. I suggested that arguments about whether or not Jesus actually prophesied the destruction of the Temple were largely beside the point. What I wanted to stress was the narrative function of prophecies like this in a text like Mark. It is all about the way in which the reader is led to recognize successful prophecy, and how that successful prophecy functions to legitimate the words of the speaker, and the text where they are found.
The inevitable difficulty, however, with an argument like this is that people do not actually hear the argument about narrative function and instead only hear phrases like "ex eventu", phrases that trigger a particular kind of response along the lines that "Jesus could have prophesied the destruction of the Temple", as if the argument had been "Jesus could not have prophesied the destruction of the Temple". Now if the discussion of the dating of Mark's Gospel is only allowed to constrain itself to the issue of whether or not Jesus could or could not have prophesied the destruction of the Temple, the argument is unlikely to move forward. It gets stuck on questions that unhelpfully draw in the writer's own prejudices about what Jesus could or could have done, could or could not have said. It is a bit like those discussions of Gospel miracle stories that get stuck on whether or not a given miracle could have occurred when the writer is attempting to reflect on its function in its narrative context.
What I am suggesting is that the way forward in this context is to by-pass the historical Jesus questions and to focus instead on literary context and narrative function, to notice that the clearest parallels to what is happening here in Mark are found in texts that post-date the events that are being prophesied. Josephus reports Jesus ben Ananias's prophecies of doom because they turn out to be accurate predictions of what in fact happened. The very point of narrating them is that the reader says, "Ah-ha -- they did not listen to Jesus just as they failed to listen to the prophets of old." Indeed, the story of the persecution of the prescient prophet (try saying that before breakfast) is one that provides a model for both Josephus and the Synoptic evangelists -- it is the old Deuteronomistic history's means of showing that the punishment of exile was an unavoidable consequence of the people's failure to hear the prophets' warnings.
I discovered Adam Winn's book about Mark late in the process of writing my paper on "Dating" and he has a helpful passage here that bears on the topic:
Much of the debate surrounding the authenticity of this prophecy has centered on whether is is an authentic Jesus tradition. The logic works in the following way: 'If it can be shown that this prophecy is an authentic Jesus tradition, it cannot be considered a vaticinium ex eventu and, therefore, Mark can be dated prior to the destruction of Jerusalem." But here, we suggest that this prophecy's identity as an authentic Jesus tradition is only indirectly related to Mark's date. Mark could have just as easily recorded an authentic Jesus tradition at a point after the temple's destruction as before it and doing so would make the tradition no less authentic. The days in which we concluded that Mark simply recorded all the tradition that was available to him are long past. We have come to recognize Mark as a creative and selective author who intentionally shaped his material. The prophecy then must be considered Mark's own prophecy that comes from either his (possibly authentic) sources or his own imagination. The focus of the debate over Mark's date of composition, therefore, should not be on whether this saying is an authentic Jesus tradition, but on whether Mark recorded (or created) this prophecy (essentially adopting it as his own) at a time before or after the temple's destruction (Adam Winn, The Purpose of Mark's Gospel: An Early Response to Roman Imperial Propaganda (WUNT, 245; Tübingen : Mohr Siebeck, 2008), 57-8).It is, in other words, a question about the success of prophecy. The prophecies embedded in this narrative that stresses the destruction of the temple tell the reader about the prophet's authority. They are, by their nature, retrospective, celebratory, confirmatory of the speaker's authority and prescience. The point here is as it is in the Hebrew Bible: the prophets told them so, and just look at what happened.