If the United States had been taken over by, say, a Pat Robertson dictatorship, and another country, let’s say Canada, had gotten fed up with the brutal thuggery of the Robertson regime, and then Canada invaded and captured Robertson and promised to restore democracy and US sovreignty, and restored civil rights, then I certainly would do everything in my power to help the Canadians and fight against the mix of Klansmen, Militia members, Mafiosi, 700 Club members, and international terrorists who were resisting the Canadians.
On the other hand, if tomorrow some country, let’s say Canada, invaded the US, started rounding up Jews and sending the to concentration camps, installed a brutal dictatorship, started looting and pillaging and shipping US wealth back to Canada, then I would do everything in my power to resist the Canadians, including paramilitary attacks on Canadian soldiers and civilian Canadian occupation authorities, and I would assist the mix of militia members, national guard, and US military that were left fighting.
In other words, the mere fact that my country was invaded says nothing about whether fighting against the invaders would be moral or immoral. An invasion that restored freedom and promised restored sovreignty would be a good thing. An invasion that crushed freedom and ended national sovreignty would be a bad thing.
And even if resisting the invasion were a good thing, violence that did not advance the goal of expelling the invaders would be a bad thing. I believe that we have a natural right to use violence to protect ourselves. But only in proportion to the threat we face. I wouldn’t murder Canadian babies just in order to sap the will of the Canadian people to continue the invasion.
So on to Iraq. What is the goal of the Iraqi resistance fighters? To force the US and allied forces to withdraw from Iraq. But why? What will that accomplish? IIf US forces pull out there will certainly be no UN peacekeepers. Even if we accept the notion, as I do, that under certain circumstances violence is justified, it can only be justified if it is in pursuit of a good goal, if then. We can all agree that violence in pursuit of an evil end is evil, right? Violence in pursuit of a good goal might or might not be justified depending on the circumstances and one’s personal beliefs, but violence in pursuit of an evil goal is never justified.
So what would be the result of a US withdrawl from Iraq? Obviously, the country would become a dictatorship again, except possibly in the Kurdish areas. Either a secular Baathist thugocracy, or a Shiite theocracy, or a Sunni Taliban-style Al Qaida puppet state would eventually seize control of the country after an indeterminate period of civil war.
This is obviously a bad result. It is not obvious that Iraq will have a semblance of democracy if the occupation continues. But it is certainly obvious that there is no chance of anything except dictatorship if the occupation ends.
Therefore, the scenario posed by the OP is misguided and unhelpful.