It is conditional, I know, I said it before, but you have to admit he said he would do it without fail. AND you have to make up some reason for why it didn't happen. God clearly and plainly said "without fail."
Let me ask you this, if your wife said "I will love you without fail," then she cheated on you, would you be so willing to look over it? Her love is conditional.. right?
I do not mean to say she would do that, and I know conditional is an overstatement here, but really... how honest are you with yourself? If GOD is sinless and a million times more holy than your wife, and if he said "without fail," and then didn't go through with it, AND ON TOP of that, he knew they would fail in doing it (because of his extensive future knowledge), then why don't bells go off in your head? There should be alarms going off, there should be some logical thought process that tells you something is up with this future knowledge thing.