It sounds like a lot of posturing to me. The rest of the conferences were ticked when TX and OK agreed to join the SEC, so the other conferences changed their minds and opposed the expansion of the playoffs. The SEC wanted an expansion of the playoffs, so this is the SEC's response.
The SEC leaving the rest of college football might happen but I'm skeptical. And I don't think it would be a good idea.
If they were to secede, I think they would be betting that most of the other big schools would eventually join them. The SEC already wins national titles in FB about 75% of the time, and they’re about to bring in two more programs that are frequently in the mix. Also notice in the article that the SEC and Notre Dame are allied here, even against ND’s kinda sorta conference mates in the ACC. That’s definitely something to keep an eye on. If the SEC (and ND?) were to break away, maybe pulling a few select Big 12 leftovers with them, the other conferences’ TV deals instantly would plummet in value. The OSUs and FSUs and USCs and Clemsons of the world would be forced to either join the new league or continue on in a glorified FCS.
Not saying any of that would definitely happen, but I think that’s what the SEC would be counting on. It’s a HUGE gamble. It’s a high wire walk across the Grand Canyon with no safety net. But the potential monetary payoff could be enormous.