That's a good question
I would ask another related question first: How long do you think we will need to wait to ask such a question? If you consider the occupation of Germany and Japan after World War II, or maybe Vietnam, should be after 5 years? 10 years? I don't think 2 years is really long enough. Iraq is progressing in some parts, but certianly still in turmoil in others, but I think it's just too soon to tell. It is prudent to think about alternative strategies in the long term. Despite what some people think, I do think Bush and his neocon cabal :-) are considering this, just not publicly announcing it, since that would be spun by some as an admission of failure, sudden U-turn, flip flop etc.