Generally, this is the way I do things:

I have several ideas about what I might do with every character. I have ideas about what I want to do with all of my stuff as a whole. These are vague ideas and they change when I come up with better ideas, or when somebody suggests something that I think might work better.

Then I have more specific ideas about what I want to do. Could just be a line, or it could be an event. Could be how I want a character to die. I remember some of these and play with them in my head, and some I write down. 

So you take something like the Rouge General. I had a plan about how he was going to die, and I knew the general rhythm of the war (when he was going to win and when he was going to lose). But the rest of it I just sort of made up as I went. I had his death scene planned something like a year in real time before I actually wrote it, but most of the other details like where exactly the battles were fought or how they would be won or lost were not really planned at all.

Similarly, I have a general idea on how I want Sahle's arc to end, but i'm not completely sure on how i'm going to get there. And I know how I want several characters to die, I just don't know when yet.