The problem is the assumption that Big 12 media rights, sans Texas and OU, will be worth more than the AAC's media rights. The Big 12 was already rebuffed by TV when asking to revisit the deal. Without Texas and OU, the media disbursement for the Big 12 may very well fall below that of the AAC.
In that light, I do not expect stable AAC schools to quickly sign over to the Big 12 - if at all. Should the ACC or the PAC12 decide to expand (maybe the Big 10 would kick the tires on ISU or KU), the Big 12 would fail yet again.
I'm not a power broker by any means, but it's hard to predict a future where the Big 12 exists.