We don't know if those insurgents would have won. At the time the prevailing belief was that there was little imminent domestic threat to Saddam. Many of the prevailing beliefs of that time were of course later proven wrong.
It's always best if a dictator falls to an internal force, because if there's an internal force that's strong enough to topple the dictator, there's an internal force that has enough strength and credibility to at least try to rule. National liberation movements often rule badly, but at least there isn't a total power vacuum.
If a dictator is toppled by an outside force that does not intend to rule, it leaves a power vacuum. Various parties then contend to fill that vacuum. The contention is not generally very polite. If the outside force that toppled the dictator keeps forces around, the contention may be fairly muted for a while, but that's not going to last forever. Sooner or later the foreign force goes home and the contending parties duke it out for control of whatever they can grab, helped by whatever sponsors they can line up. I don't see how any of this is a surprise.
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