Indulge me a moment.
I doubt Allied forces will ever definitively know if Saddam is dead. We have no DNA of his to test, unless we round up relatives and start testing them.
Concerning the doubles of Saddam, I would question if doubles were meant to be used on TV for speeches, etc. Would they not best be used at a distance or in a fleeting glance, as a car drives by a certain point. Anyone at that point would get not much of a glance, but quick enough to consider that the person in the car might indeed be Sadaam. One would think, unless the double was indeed trained to speech as Saddam that indeed, the person on the TV was not the "real" Saddam (I don't think a double would be used to read poerty).
I personally lean torward the theory that it was Saddam on TV, just taped earlier in the day, as he had done that in the past.
With that said, it is still possible that Saddam is injured or dead (i.e. not in authority). I do not put as much stock as perhaps I should in Republican Guard units surrendering as a reliable sign that Saddam is not in authority. They are too distant from Saddam per se to control without the help of the Military Intelligence Service (al-Istikhbarat al-'Askariya). This organization has informants which keep track of loyalty within military units. I remember reading yesterday some decree concerning Iraqi forces that deserters wouild be shot. I'll have to find the article, but I wonder if that message came from the Istikhbarat.
What would be vital to know is if the Special Republican Guard units are starting to desert or surender. Certainly a more elite unit, it took over the original mission of the Republican Guard and is the garrison for Baghdad. Most of the solider in the SRG are from Tikrit and the surrounding towns, so they are more trusted by Saddam. I would also want to know if the Palace Guard units are deserting or surrendering.
If Saddam is unable to give orders, one will also expect his faithful in the Bayjat clan to flee to Tikrit, one his Saddam's strongholds. We shall see.
If indeed others were injured or killed, including Abid Hamad Hamud, Saddam's personal secretary (and leader of "The Companions"), there is truly a leadership vacum. Senior Iraqi military commanders would now be fighting mainly on intent - I don't think there was much of that taught in Iraq, as Sadam wanted (and needed) to control all aspects of the military (to ensure no coups could be successfully undertaken).
Of course, Saddam could be alive and laying some sort of ambush, but I wonder if he is that creative a thinker under high stress situations. Maybe - he knew the allies were coming in, they would not be stopped and perhaps has consider the persistent reports on bin Laden being dead/alive/whatever. Perhaps he wants to kill as many Allies and his people as possible, in a smaller area that a desert battlefield and maintaining a low profile is one way that he believes that can be done.