Would Bush have won if he was up against a black person?

What if is a difficult thing to answer because hindsight is, as they say twenty-twenty. Bush would have probably won anyway, which would have made the second part of your question a moot point. If a Democrat had been elected and served the same eight years, it is likely that a Republican would be elected, but it is doubtful that John McCain would have been put forward as the Republican candidate.