I'd rather make sure they are killed. Big 12 has been wounded many times and has come back.Perhaps the more likely angle is to kill the Pac as a future competitor. But maybe that isn't necessary either. With USC and UCLA gone and no great expansion candidates, maybe the are so wounded already that they won't ever be a threat to the B12.
I'd like to take CU, AZ, ASU, and San Diego State (assume Oregon/Wash not available). San Diego State over Utah to give California presence and the fact Utah has been the biggest Big 12 basher out there. Plus, the con for CU, AZ, and ASU going to the Big 12 is that they have a lot of alumni on the West Coast, particularly the LA area and San Diego State helps address this a little bit.