Cruz should consider Trump for Secretary of Commerce. That’s about it.
Cruz is not going to be the nominee, and if he was the Republican party would do everything in it’s power undermine him. They would rather have a Democrat president so they can keep their lock on the party and use the threat of a Democrat president and a Democrat congress to blackmail conservatives to vote for them. Then when Cruz lost, they wwould blame it not on the fact that they abandoned him, but on his being “too extreme”.
Of course they will try that with Trump too, but unlike Cruz he doesn’t need them. He has the money and personality to go over the heads of the GOPe and persuade the public directly.