I can promise you, that Illinois vs. Indiana will never be one of the Network games. We may get an Illinois or Indiana vs. OSU/PSU/Mich/MSU, but never against each other.
As far as OSU visiting USC, that game will simply be on CBS/NBC. That's why it's very appealing to both CBS and NBC to be in on these rights. When a team like OSU/PSU/Michigan/Nebraska/Wisconsin/MSU travel out west, those are great games to have on your network. Fox will still get a great game. It wouldn't surprise me to see the B1G have a game like Michigan vs. PSU/MSU the same day OSU travels out west. The B1G can be very creative with how they work up the schedule to maximize all these tv windows for their television partners. Also, OSU is probably only traveling to USC like once every 6 years, so that wont happen very often.