I'm far from an expert on realignment. I'm intrigued but don't keep up with it as closely as others. That said, to understand realignment, I think you have to understand primarily two things: (1) how much money a university is bringing in and (2) how does it compare academically to its fellow conference members.
Currently, I'm not sure how Duke ends up with more money in the Big 12, provided it enjoys a portion of any large exit fee/GoR settlement from departing members, and provided the conference TV and CFP money ends up being similar to what the Big 12 gets. And academically, Duke doesn't fit in with the (mostly) rabble in the Big 12. Nothing is impossible, but all signs point to Duke staying with Cal, Stanford, ND (at least, for now), Georgia Tech, and other AAU institutions (Miami, possibly USF later).
Note that for FSU and Clemson, they don't necessarily see things this way. They care less about academics and more about money/access, which seems to be driving their current attempts to get out of the ACC. In fact, that's been their frustration all along - they care more about athletic success than the other denizens of the ACC, but all of the other teams benefit financially from them. But I suspect the president at Duke is more concerned about academics and fielding a strong basketball team and good, but not necessarily great, other teams.
Again, nothing is impossible, but that's my take on the Duke rumors.