I'm sure they'd be happy about it, but I doubt they'd throw a huge celebration either.
Sports fans have a tendency of pretending to know people's frames of mind and base their opinions off of their assumptions. (I'm guilty of this myself sometimes)
I'm positive that CC and the Brewers would like this to be overturned because it'd be a good mark on CC's record, but I doubt they're going to be pissed or anything if they don't overturn it.
I'm sure if it was a matter of him either having the no hitter or the Brewers still being in the pennant race they'd choose the latter 7 days a week and twice on Sunday, but that's not the case. They're in the pennant race and CC threw the gem whether they overturn the ruling or not.