If Cruz loses Iowa or loses overall, he has another 4 years to run again. He's young enough.
He will be primaried in 2018
By who? An establishment challenge would be a disaster in Texas and there is no room to Cruz's right.
Cruz was only able to win in 2012 because of the liberty wing. Cruz is becoming increasingly more mainstream. That will not resonate with all Texans back home.
Less libertarian =\= more mainstream. If anything, Cruz running as Trump-lite will only increase his popularity with the anti-establishment crowd in Texas.