If the US couldn't find a way to extort a Status of Forces Agreement out of Iraq's government before the expiration of its UN mandate on December 31. The US would then be, without any cover of international law or UN approval, an illegal occupier of a foreign nation. Any killings by US troops thereafter, I believe the law would say, would be murder; and those who ordered the occupation would, one would think, be culpable, just as culpable as Hitler was for the deaths that occured during Gemany's illegal occupations during WWII.
I'd paddle to the Hague to be inside the courtroom to watch the trial of Bush/Cheney on those charges. Hell, I'd even resuscicate my dusty old shingle if there was a one-in-a-hundred chance I could participate in the trial, if only to fill the prosecutor's water cup during final argument.