from my OT class

So I have this Old Testament class, and we are going through the book of Genesis right now, and the professor mentioned the story of Abraham as being understood by some as allegorical, thus not real. He then posed the question "If Abraham didn't exist does that mean Christ didn't die?" Obviously this was to get those with a "traditional" or "conservative" theological stance to think (or annoyed).  Well I'm always up for a challenge even though I don't think of myself as solely traditional or conservative.  The question is interesting, though, because many in fact would argue that if we say one part of the Bible isn't  historically factual that then has a direct correlation to the story of Christ and now the story of Christ becomes totally and completely untrue.  I don't think it's necessarily that clear cut, but I am nonetheless piqued by what allegorical understandings can do to Scriptural interpretation and understanding.
I'm posting a copy of my response to the discussion board, but before I do that I must feel I must explain that it is indirectly responsive to the other two responses as well as the question.  They argued, essentially, that there is a bigger theological understanding to the text, and the one can know Christ and experience transforming faith through him without having to worry about the nature of the Abraham's story.  Now this view I understand, but mostly disagree with which is what my post is more about; I think the posed question is not dealing with how such a reading impacts of experience of God's power or one's faith.  Therefore, I am more concerned with how such a reading impacts the whole flow and understanding of Scripture and the implications that a particular reading in one place has on another reading in another place.  Also, this was literally an off the cuff sort of thing, so I must add that it is definitely lacking:

The story of Abraham doesn't correlate, necessarily, to whether or not Christ died, it does I believe correlate to the resurrection.  The power and authority of the resurrection does not come solely from the story of Christ and the writings of the New Testament, but from the Old Testament and the story of Israel. The problem with understanding the stories such as Abraham in a new light is that you must understand that in light of how it can impact the story of Christ.
If we are to say that the story of Abraham is only allegorical it can be understood to be the express of humanity's longing for God to redeem his creation.  The idea that God has an intent to bless the whole world.  That God sees faith as our righteousness and not our actions.  The idea that God will provide the offer, such as in the story of Isaac, that culminates in the Father doing with Christ for everyone which he would not let Abraham do only for himself.  It can, however, run the risk of understanding the story of the resurrection in the same light.  That resurrection doesn't actually happen, but it's allegorical, and as such expresses the human longing which we can experience through the story and lifestyle of Christ, which raises another issue in itself.
Another risk that a pure allegorical reading can render is that actuality of God's work.  If the reading is purely allegorical then we cannot point to the work of Christ and say, "Look what God does for us!", and then point back to the story of Abraham and say, "See he's been actually doing it all along!"  The allegorical reading sacrifices a sort of evidence that we can point to showing that not only has it long been humanity's longing, but God has long been fulfilling that longing.  The allegorical reading cannot say that God hasn't been fulfilling our longing, but it can prevent us from showing a certain sense of "proof" of where and how he has done it.