So... it sounds like this is all highly speculative and very preliminary, but here's how I see it if it were to shake out:
1. ABC would likely hold on to ESPN's network broadcast rights for some period of time after the purchase. ESPN would produce the broadcasts and ABC would license them (potentially through their next contracted Super Bowls). Kind of like how Hulu still has shows from Fox and NBC even though both sold their Hulu shares to Disney. I don't know if it would be for the full 10 years of the SEC contract with ESPN.
2. If/when the ESPN agreement with ABC/Nexstar ends, the SEC ESPN deal looks a lot less appealing since it removes linear OTA broadcasts, which is a key component. Suddenly, the Big Ten, Big 12, Notre Dame, and ACC have national OTA broadcasts and the SEC doesn't.
3. I think this would be the point where ESPN goes full speed ahead on streaming and uses that as a bargaining chip to keep the SEC (and its other licensed partners) happy. Alternatively, they'd have to shop ESPN produced broadcasts to the networks and they all seem to already have pretty full Saturday broadcast slates.