You responded: That's the beauty of teaming up with al-Qaeda, from Saddam's point of view. There are guys sitting here right now who are just itching to get the combination to that locker in Grand Central Station, so they can get there 72 virgins. They are not going to be intimidated. They want to bring it on, and only Saddam is holding them back.
So who has the combination to this hypothetical locker? Saddam Hussein and maybe one or two people close to him. If Hussein were assassinated, why would one of these other people release the combination to al-Qaeda operatives, knowing that it would inevitably lead to the end for him? Assuming the person holding the combination is not a suicidal maniac (but is the ordinary kind of maniac that runs dictatorships, someone who is interested in his own personal survival, success, and power), deterrence would work to keep him from acting.
The biggest danger is in not acting quickly when the time comes. If Saddam Hussein sees himself being slowly defeated, he'll have the opportunity to activate his sleepers. For this reasonm, he must be defeated quickly and with no warning.
By that logic, the US and Soviet policy of MAD was just a mirage: nobody could ever be trusted to loose off nuclear missiles in the event of a decapitation strike. But, in reality, conditioning soldiers to be loyal to their leaders, even under the most extreme circumstances, is not a particularly hard problem in human behaviour management -- it's one that has been overcome by every regime in human history. The system doesn't have to be perfect, there don't have to be just one or two people involved, they don't have to be in the line of fire for the retaliation, and the system doesn't have to be proven 100% to function as a deterrent. This how the United States and the Soviet Union solved that problem, and Saddam is merely following their lead.