Scourge will stay until he is sure the Emperor left us no surprises.
A more frustrating "dissident companion" is Ashara. If you're a DS SI she's the equivalent of a LS JK's Scourge- can't change her and probably don't want her on your ship. The fact that a SW can have Jaesa go one way or the other likely means the thought was there, it just wasn't further implemented.
Yes and no. Ashara is more logical than anything. I used her on my DS Sorc more or less from 35-50 and managed ~7k Affection without gifts. For example, if you blow up an orphanage because it's fun, she will hate it. If, however, you can provide some sane reason it's necessary to blow up said orphanage, she will like it.