First, I need a jury in Lincoln. Second, I don't know anything about the actual language of the grant-of-rights, but there's no way that any school signed up for the grant-of-rights with the understanding that the conference could prevent them from playing football at all. That's not to say – importantly – that any revenue hypothetical OOC Nebraska games generated wouldn't go to the Big 10. But I highly doubt the grant-of-rights prevents Nebraska from playing football.
I have a strong intuition that the reason this isn't happening has nothing to do with the legality of it. It's all political. It would be incredibly embarrassing for the Wisconsins and Penn States and Michigans if Nebraska played games without incident. So they're leaning on Nebraska's decision-makers to stay lock step. Just imagine if Nebraska played, generated millions in TV revenue, and then had to share it with teams that weren't willing to take the risk. The political fall out would be significant and it would have a long term negative effect on conference stability.
All of this just demonstrates why conferences have gotten too big and too powerful. Need to go back to 8-team conferences, based on regional match-ups, and screw TV money. But to do that in a competitive environment implicates collusion and antitrust issues. It could be done, but would require a lot of political will – political will that of course doesn't exist since the AD's and coaches who typically make these decisions are paid ever-increasing salaries from those same TV dollars.