First things first. Is Cruz even on the list Trump has already drawn up ?
Cruz probably doesn’t want the appointment. He very likely hopes to ride the political waves and surf into the presidency in either 2020 or 2024 depending on how things go. He is only mid-40s, plenty of time to ripen on the vine and rebuild his position as things evolve. And it could be a good thing even from an ardent Trumpian point of view, no telling how smooth the transition might be by 2024, but obviously Pence will be a big player too if he wants to be, even a good-boy Ryan could rehabilitate himself over time.
Eight years is a lifetime in politics. Right now, Cruz has more to gain than lose from a successful Trump presidency. I would expect him to realize this and act accordingly.
However, if he were to be appointed, it would be a lot better than a kick in the head. As to the idea coming from Lindsey Graham, the man walks upright so he has had at least one correct idea in the past.
Nope.