Will they be working if they've been shot? Will it gain the support of the people? The answer to both is clearly no
I grant the first point, not the second. Why is the idea that people will support (or at least resign themselves to) a government which shoots protesters so clearly false? Please do not tell me at this point "Look at country X." I'm looking for causal explanations, not historical ones.
so if they do fall back in line it will only be temporarily, like until the invaders appear to have more strength.
Here you are assuming in the first place that the terrorized people are not actually terrorized, but simply quietly, rationally biding their time, waiting for an opportunity to strike. In other words, you are assuming that you cannot actually terrorize people into submission. Is this accurate?
In the second place, you are assuming that the government cannot manufacture opinion about the strength and chances of the enemy long enough to ensure that the invaders never appear strong enough to make the oppressed masses think the government can't suppress a rebellion.
In the third place, you're assuming that either a rebellion would enable the oppressed masses to actually become free, rather than just falling into the clutches of the invaders, or that they would prefer to be the subjects of the invaders rather than the present government. Moreover, you're assuming that the government cannot put out persuasive propaganda to the effect that no matter what you think of the them, the invaders are a thousand times worse.
Moving on, I have never assumed that any of the statist countries involved were highly centralized. They could well have large free-market economies, merely subject to a state. You have to make the argument for the efficacy of resistance on the basis of the worst possible assumptions about the enemy. After all, if the invader launches a nuclear missile into his own country, the anarchists can successfully repel him, but I assume you'd like to be secure against more than General Schultz.