Had Brock stayed who knows where Batista, Cena & Orton would be now. Remember when Brock was the main event guy so was HBK, HHH, Benoit, Big Show, Angle, Goldberg, Eddie, Booker T, Undertaker and a few others, it always goes along with Edge. It could all be different right now had Brock stuck around, nothing says Cena, Batista, Edge & Orton would be where they are now.
I think Cena though would of been a big star no matter what, cuz during that year he had some nice feuds with Brock & Undertaker. But as for Orton & Batista I think there rise only came because of Brock being gone, hence Orton becoming the youngest champion ever only a few months after Brock left. And then Batista winning the world title a year later at WM vs HHH, in a match IMO it would of been the first 1v1 match of Brock vs HHH. And Batista would still be a mid card guy if any.