A republican governor could be elected in Illinois - in the last election the current governor barely won by just 19,000 odd votes. Or a pro-gun democratic governor could also be elected.
As a former IL resident, I can tell you that the 'R' or 'D' next to someone's name doesn't really mean much, what's more important is what part of the state the politician in question is from. Generally speaking, the closer to Chicago the politician's home is, the more anti-gun he or she is.
The last governor of IL that I could see supporting CC was probably Jim Edgar, a Republican from Charleston. The following governor, the now-incarcerated George Ryan, was a Kankakee Republican and rabidly anti-gun as are his successors the also-incarcerated Rod Blagojevich and current Gov. Pat Quinn who are both Chicago Democrats.