In the grand scheme of things, if Mizzou goes to the "little 11", there will be little or no impact felt by the Big XII. I didn't bring any flow charts or lists of revenue to this discussion, but this scenario wouldn't suprise me in the least.
So, Mizzou leaves the Big XII (boo hoo) to go to the Big 10. The hierarchy within the Big XII have probably been thinking about this for a while, so they have a plan to intercede, ready to go.
There are several attractive teams in the non Big 6 conferences, that i'm sure could be easily lured into joining the Big XII. TCU, Houston, maybe even Utah, could possibly be coaxed into joining. Especially TCU or Utah, considering the fact they're past foray's into BCS bowl games with good records and not playing for a National Title. Now, considering the competition they will be facing will make it increasingly difficult for them to go undefeated, and play for a NC, the fact that the opportunity is more feasible, being in one of the Big 6 conferences, should be more than enough to entice them. (not even thinking about the increase in income)
I surmise that if anything, Mizzou leaving could make the Big XII, a better conference.