There was absolutely zero chance we would have ever ended up in the mountain west.
100% chance we were Big East bound had crap hit the fan
Big East may have been an option, but it was much more likely that the remaining 5 schools would have stayed together and invited new schools into a new Big 12. When schools leave the conference, they forfeit their voting rights. Including on matters such as dissolving the league. So the remaining 5 schools could have voted to keep the league (and its name and BCS status), collected exit fees from the other 7, and then invited 5-7 new schools.
Keeping the Big 12 together with the Texas/Oklahoma schools was always plan a, the revamped Big 12 with the Orphan5+new guys was plan b. Big East was out there as plan c, but really only if super conferences started to form.
And as I have said before, in all 3 plans KU and K-State were working to stay together.