Canonically she doesn't really, and she certainly wouldn't want to live if it meant harming Sakura.
I think it's much better for Sakura to regain control of her.
i don't see how getting another master would hurt sakura.
Well, Sakura is still a master, for one thing, and thus a potential danger to any
new master. Also, killing Rin and Shirou would harm her. Even if Rider is willing to do that to protect Sakura's life, I don't think she would do so for her own benefit.
I'd like her to have an actually decent role in the story, like Rin and Shirou do.
there's the same type of role and there's a decent role, the two aren't always or often the same thing.
Perhaps, but in a Grail War the masters are always going to take centre stage.
I really think removing Rider from Sakura's control is a bad idea.