Not 'forget' forget.. just he would fade into the background like Busby did. Busby is still a legendary figure, but whilst Fergie was successful.. the fans were focused on what Fergie was doing, not harking back to the past.
Right now, he looms as a huge figure over the club and the likes of Moyes and Van Gaal have made us miss Fergie even more. We need to move on from Fergie in the same way Liverpool had to move on from Shankly.
It is not easy for managers like that to let go. They think that they can easily handle leaving a club behind and move on.. but having held on to power for that long, being seen as the man.. it isn't easy. It isn't a character flaw, it is human nature.
Last thing I want to do is attack Fergie.. I love the man, I'd love to see a young Fergie back at this club. I'm just saying in my opinion (opinion not fact) that he is much more likely to be looking after his own interests than someone like Charlton who is just a much more different personality. Charlton has proven in the past that he only puts the club first, he's a traditionalist yes but he isn't a man who needs to embellish his legacy..nor does he seem the type to concern himself with stuff of that nature.
Fergie openly loves his politics, he openly admires power and the control of it.. so it isn't such a big deal to assume that he could concievably find it hard to let go of any influence on what was once his 'baby'. We've seen it with other managers such as Shankly, Stein and Busby.. guys who Fergie is incredibly similar to.