Hence "almost certainly." In a way, it would have been even harder for him to back down than LBJ. And what people don't realize is that a lot of Civil Rights legislation wouldn't have happened without the assassination, because LBJ--that wily old Texan--was able to say, "We must pass this legislation to honour our fallen leader!" Except Kennedy hadn't really cared all that much about it. He used it to make political hay, but he didn't care as much as Bobby, who at the time didn't seem to care as much as LBJ.
Actually, I've begun to think that Bobby was the more interesting of the two. Jack was trying to fulfill their father's need to have an Irish President. Joe, Jr., had died, so it was Jack's job. When Jack died, I think Bobby underwent a lot of political changes, and I think he came out the other side a better person. I think he went from seeing the Civil Rights Movement as a tool to actually believing in it, for example. But we'll never know about Bobby, either, because an alumnus of my middle school stopped his Presidency before it got started. Of course, we'll also never know if he would have won.