Cruz is much much more intelligent than Trump. Cruz isn't going to endorse him unless he has good reason and it benefits the country. That's been Cruz's objective; to restore the Country under the Constitution. The way I see it ... the Donald needs Cruz right now more than Cruz needs him. On the surface, Cruz has everything to lose by endorsing Trump and nothing to gain.
And what if Trump were to announce that his SCJ nominee to replace Scalia will be Ted Cruz...and that the nation needs a man like Ted, with his admittedly extraordinary legal mind...on the court. Part of this transaction would include an endorsement of the GOP nominee, of course.
What then would Ted do?
My guess, he would accept, knowing that his presence on the court rather than an extreme liberal filling Scalia's shows...would be of far greater importance than any issues of hurt feelings and/pride.