Barry Diller used to be on the other side
Barry Diller used to scream "illegal" until he bought Aereo. Nothing is right or wrong, it just depends on who it benefits.
I can't see them going off the air. All the networks already own multiple cable channels. What good would it do to have another cable channel? They could just transfer their shows to the existing cable channels. If the existing cable shows can't come close to the highest rated network shows, why would it matter if they have another cable channel?
I could see the networks cutting out their affiliates. They would broadcast OTA from their owned and operated stations, and then just post the shows on their websites with a live-stream at the same time. You wouldn't need Aereo because the shows would already be there.