It's "then" thinking. It's "now" thinking. And given Trump then my position is "right" thinking. No president under the best of circumstances will allow a veep to take attention away from the him. In eight years as veep to a narcissist like Obama the only time you heard from Biden was when he screwed up or when someone died. And Trump of all people is less capable of sharing the center stage. Trump will do what Trump wants to do, his policies will be what he decides, he doesn't take advice and he doesn't take disagreement from anyone. Under him the vice presidency will be worth even less than a bucket of warm spit, at least as far as the holder of that office's ambitions are concerned. Eight years as veep would be eight years wasted for Ted Cruz. Eight years of breaking ties and going to funerals. If he doesn't get the nomination then I could see Cruz stay in the Senate where his opinions and actions matter, and perhaps run for Texas governor and then the presidency again in 2024.
The point I am trying to make is that for Conservatives to have one of our own in the Executive Branch (and presiding in the Senate) changes the game as it has previously been played. We (and our aligned media) would have a focal point to rally and Cruz would have his own Bully Pulpit.
I guess the real question is whether a candidate who has, thus far, not exactly addressed fealty to the Constitution (Trump) would even want the man who does exhibit such fealty (Cruz).