As far as I know they're not even returning to Chicago, so they will kind of be forced to film a new look anyway.
I was referring to the gif 'herolee' posted, which had nothing extraordinary in the shot beside the falling, fiery car. It was an empty street, with empty cars strewn about. That's what I mean when I say it was relatively easy to capture that specific shot on-location.
As for the overall destruction, then yes, of course that would have to be CG. but there's something to be said of compositing (see
Elysium's LA or
Dredd's Mega-City) rather than all-out computer imagery. A viewer can easily tell the difference in quality, without necessarily knowing the technicalities behind the shot.
Plus, I think Bay proved three consecutive times it's absolutely possible to wreck city blocks for real. But there's no one quite like him, so perhaps that is an exception.