Not any more than anything has replaced anything else. Hell, even MySpace is still going. I don't think that FB "killed" MySpace; it's just that it happened to be gaining traction when MySpace was starting to implode on its own.
Some people will like G+ more than FB; some not. I'm using both and have my likes and dislikes of each. <shrug>
Agreed.
It is too early to talk about the possibilities of G +. Let pass at least six months. Then we can say that this is just a toy, and soon all get tired of it or it is a real competitor which can replace FB. My opinion is, G + will do nothing radically new in the social networking what FB can't do. So, G + started quickly, but late.