He won't go back. Bollocks is too busy being an asshole to the media, a womanizer and enjoying the cash flow at Chelsea. If he were to move to Juventus, he won't be taking any pay cuts.
I don't know honestly, but they might be interested considering that Mauro Camoranesi and Pavel Nedvěd are going to retire in the next year or so. What will they be left with if they sign Ballack though? More aging players past their prime.
I did this once in Football Manager and it worked astoundingly well. However, I don't see the point. As M21 already pointed out, Ballack is getting old and Juve need to bring in some young midfielders for the future.