The Utah invite removed BYU's only reason to remain in the MWC.
I suspect that discussions with the WCC were about the time that BYU started having similar discussion with the WAC. It may be a bit of a stretch to assume that BYU put all their eggs into one basket (the WAC) given the rapid changes in conferences at that time. They probably even put out some feelers to the Big West sometime during that period of Jun - Sep 2010.
I notice that no mention was made of the Big East expansion attempt that proposed to grab BYU, BSU, & SDSU for football at least. That was a viable alternative until the Big East also got raided.