More so a PAC 12-Big 12 merger than a PAC 16 Plan B, you could take the:

PAC 12 - Ore St - Wash St + 6 Big 12 schools

Quad 1: Cal, Stanford, USC, UCLA
Quad 2: Washington, Oregon, Utah Colorado
Quad 3: Arizona, Ariz St, Texas, Texas Tech
Quad 4: Iowa St, Kansas, Oklahoma, Oklahoma St

You could rotate the pods or do permanent divisions (in which case the AZ schools would be in the West and Utah and Colorado in the East).

12 of the 16 are AAU.

If money is what Texas and Oklahoma are after then they should obviously look to the SEC/Big Ten but if they want to be the power programs of a conference but the Big 12 as is isn’t enough of a money maker to stay in proximity to the Big 2 then this might work.