That was the catalyst but was it the root cause of the instability? I think an argument can be made that a house built on an uneven foundation was going to fall as soon as the conditions were right. Nixon started the conditions.
The root cause was when the B1G announced expansion and Notre Dame rejected them. CU to the PAC and MU to the B1G were looooong open rumors back to the Big 8 days. There was no instability then. Both were more prestigious conferences at the time and Big 8 was a smaller one. CU had the better cultural fit, too.
So when B1G got rejected, MU was completely obnoxious about them leaving for the B1G, which created the instability. MU "leaving" and CU leaving then started NU to start looking around and got poached. The following year, MU left (while chairing the Big 12 expansion committee), left for the SEC due to "instability," which was created by them and continued with them leaving.
Don't get me wrong, I'm not disputing uneven foundation had a hand in it, since it did, however it's hardly the root cause. Yes, unequal revenue for UT, A&M, NU, and OU stunk, however it was slanted in the Big 8 days as well. However, CU and MU leaving wasn't caused by Texas. NU and A&M leaving may have been caused by Texas, however they got beat at their own game and they left after the MU to B1G debacle.
Honestly, a good "what-if" scenario would be what would happen if ND accepted the B1G invite. Would the other conferences have expanded? I bet we'd still have NU and MU if ND went to the B1G. (I think we still would have lost A&M and CU at a later date.)