The Pac12 is currently going to be at 10 schools after this season, losing USC and UCLA, one can conclude that SDSU and SMU have been told they are going to be the two replacement schools for the two leaving. So, telling the MWC that they are leaving next year, before the end of the month is going to save them around 15 million dollars. SDSU will play in the MWC conference this year, just as planned, and then after their TV deal is finished both schools will be announced as the two new members of the P12.
No way Oregon and Washington sign a long term GOR of more than 5 to 6 years. What Colorado or Arizona do will not affect SDSU and SMU joining the league at all, they then become the 9th and 10th members as opposed to the 11th and 12.