You honestly think Cruz would give up a senate seat for a place in a Trump cabinet? Yes
Really? Yes
Maybe I need to include a disclaimer. I do not personally know Ted Cruz and in any case I am in not in a position to represent him.
Why? I think that there is no doubt that Cruz wants to be president. When was the last time a cabinet secretary moved to the presidency?
Given his ambitions there is nothing to be gained for Cruz by serving in a Trump administration, either in the cabinet or as VP. And because of that there is no way Cruz would accept any offer Trump made, and no reason to believe that Trump would make any offer in the first place.