First, a school's administration isn't going to green light a vote to dissolve without having something firm lined up. Too many people have to give it the go ahead, and institutions don't leap blindly with that big of a decision. A few schools are pretty much guaranteed a spot in the B10 or SEC, but getting to 8 is borderline.
Second, having a backroom agreement is a conflict of interest. Failing to disclose that conflict of interest invalidates the vote, and sets up the left-behind schools for a massive lawsuit that's a slam dunk. A deal like this would include at least 8 schools, 2 networks and 3 conferences (and their 44 member schools). That means a lot of people would be involved in even an informal deal. What are the chances they can keep it all under wraps and have nothing in writing?