Missouri did no submit a letter of conditional withdrawal nor did it notify the conference on Monday of plans to leave.
The Big 12 Board of Directors met on Monday, and the hope for everyone in the entire universe was that Missouri would end this national nightmare. However, the wait continues for basically every school associated with the Big 12, SEC, and Big East. Missouri still seems to hold the fate of WVU, Louisville, Cincinnati, and possibly BYU as well. If they go, then a whole new round of debate begins about which one of these teams is best suited to fill Mizzou's void.
However, it may be a moot point if the Big 12 does decide to go 12 teams. In the scenario, it seems likely that WVU and Louisville would both be heading out of the Big East. And, if Missouri is gone, Cincy or BYU could be that final team.
If Missouri stays, then look for the WVU to SEC rumors to fire back up, which will really be good for nobody. Even though it makes sense, there hasn't been any concrete evidence that the SEC is a huge fan of bringing the Mountaineers in.
So, again a big thanks to Missouri for keeping the ridiculousness of conference realignment alive by holding out as long as humanly possible, and completely messing with the fate of half the country.