As long as the conference doesn't lose all (or all but one) members, it will still be P5. It may be at significant risk when the CFP expires, but if these loses are dragged out and the Big 12 only backloads with a small number of quality football programs, they could survive into the next CFP contract.
College administrators are extremely conservative when it comes to changing contracts and it seems unlikely that they would try to punish the Big 12. They have had several chances in the past to establish the precedent that conferences should be punished for realignment losses and never attempted to do something like that. A big reason for this is that if such a precedent is set, that precedent could come back to hurt the other conferences. Hence the reason no one wants to make this a precedent.
Also if the number of playoff slots equals the number of power conferences, that would guarantee some kind of anti-trust lawsuit which works towards the Big 12's favor. The P5 want to avoid a 4-team playoff, four power conferences scenario.
The financial hit wouldn't be that bad. The conference has pro rata increases/decreases meaning that whoever they lose or add in their current contract, the payouts will stay the same. Plus never in the history of conference realignment has the current tv contract been revoked for realignment losses. There are two cases where a conference made less money on the follow up contract. But in both cases that was the result of the conferences losing all but one school. So there is a chance that might happen to the Big 12 however I seriously doubt they lose more than 60% of their membership.
So even if they lose around half their schools, they make the same on their current contract, on their next contract they either keep the same rate or make a small gain, but the B1G, SEC, etc. see huge increases. The Big 12 is still going to be fine. They can make up a big chuck of that revenue gap with postseason payouts which are divided by conference without accounting for number of teams. So an eight team Big 12 gets the same cut as the Pac-16.
So to answer the OP. The Big 12 will be fine even if shit hits the fan. The only scenario where they are not fine is a scenario where virtually every Big 12 school finds a home in another P5 conference. So for Big 12 fans, you don't need to worry all that much. However this only happens if the Big 12 doesn't "replace the cream of the AAC." They should use their small size and quality to an advantage. Don't dilute the brand with inferior schools. Only add "sexy" programs that are generally respected and competitive such as BYU and Boise State. Wait for another Utah or TCU to emerge before settling on other schools.