Many evil dictators commit atrocities in order to gain the power they want. Of course then they want peace because that's what protects everything that they have gained/stolen. I haven't read the book so I don't know this Galbatorix person. But from what's been said, this person is still evil. Therefore, there isn't anyway he can govern, in my opinion, in a way that doesn't cause harm to anyone. Every decision he makes will be based on benefitting someone over someone else. That's what politics boils down. And if he did all these things to take over then he is most likely in possession of a lot of resources that should belong to other people and it would positively impact their lives if those resources were returned; either to the families who lost them or given to the poor.
There is a dangerous cycle in which the rebels turn into the next empire. So if you help them it's like you're helping the new Hitler beat the last Hitler. This would change nothing so if that was the case I would stay out of it and maybe politically attack both sides. The question is how do you know? You'd have to know the heart of the leaders. You'd have to know what they're fighting for and judge the value of their end goal vs what they've done and what the future will be like for the common person. The republicans in the US ranted about how terrible "Obamacare" was to the point that many people didn't know it was another name for the "Affordable Care Act" which was quietly saving a lot of lives and helping a lot of people get the coverage they needed. Now that they are in a position to replace it every solution they come up with sounds monstrous and would likely kill people dependent on the ACA.
I don't think you can blindly follow anyone. I think you have to start from a place of high moral values as a platform and push from there. It's not enough that freedom fighters just want freedom or just want to take out the dictator. If they don't have strong discipline when they get power they will likely fall to corruption as well. Sometimes you have to be patient. And maybe if the powers that be aren't using dramatic means then maybe you shouldn't either. Maybe there are systems within that government that you can work within or maybe he has children who can be positively influenced. I think the biggest issue is the arrogance that we tend to use to justify our positions; thinking that we're always right and therefore evil rides in on our backs.
