A straw would imply it was one thing among many, not impulsive.
True.
But the real debate at that time was about conference
survival, and it's hard to envision, regardless of the results of that game, Nebraska being in a position to survive as what we now consider a P5 school in the Big 12 had half a dozen schools actually left the Big 12 at that time. It's very possible, had those schools left at that time, that there are now four and not five power conferences, and very possible Nebraska joins the Big 10, anyhow.
Of all of the schools that eventually left, Nebraska is unique in this regard. Nebraska is also unique in that they were given an ultimatum....agree to the conditions of the conference, which tended to favor Texas, or get out. Nebraska decided to be proactive and leave, rather than let their fate be decided by others.
Rather than a "final straw" scenario, I could better see that game maybe having enough of an impact that it may have swung the eternal power struggle enough to Nebraska to avoid being more or less forced out. At the time, it was very one sided towards Texas, though. And, it's not a stretch to say it had been since Texas joined the conference. Even in an ideal scenario portraying Nebraska as conference darlings, flipping positions with Texas, remember Nebraska was being utterly destroyed in matters of conference voting. And, while Nebraska does well in regards to athletic revenue, Texas and Ohio St are in an entirely separate realm from the rest of college football.
In the 2010-2011 school year, Texas had a revenue of about 150 million, 18.5 million more than second place (Ohio St). They were way ahead of anyone in the country, much less the conference. That equates to a lot of power when it comes to conference politics and realignment. To me, they were such an economic juggernaut at the time and therefore were wielding so much power, an alternate ending to that game or that season doesn't change the relative positions of the schools enough to alter the final outcome. Obviously we know this now in hindsight, but it's worth noting anyhow...Texas took their downturn not long after that season, but they still remained huge at the box office. That suggests, for purposes of this discussion, that Nebraska wasn't likely to see much of a relative change to Texas in this regard had that season flipped.
For me, to put more credence into this alternate reality theory, I have to see results of that game/season altering Texas' supreme position of power and envisioning Texas not looking to push around Nebraska in matters of conference voting and potential realignment. The history of the Big 12 conference simply doesn't suggest that would happen. Texas joined at the height of Nebraska's conference influence and still got their way on nearly every matter that separated the schools.