That is why candidates drop out!
When a candidate is mathematically eliminated from getting the majority of delegates he acknowledges defeat, he doesn't plot to take the nomination to the convention.
Candidates drop out when:
1. They realize they have no chance at winning the nomination under any circumstances.
2. They run out of money.
Neither of which apply to Cruz. It is not unreasonable to believe that Trump can be held to less than a majority on the 1st ballot. And, given a contested convention, it is not at all unreasonable to believe the advantage may slide to Cruz.