Seriously?...Are you serious?
That is an outlandish statement!
....and so very far from reality
The proof is in the pudding. That is, if Trump *does* offer him a powerful position, one worth leaving the senate for.
Do not underestimate the value of having a universally hated hatchet man to do the dirty work. Much of the venom that would be directed at Trump would instead be directed at Cruz; and those opposed to what Cruz was doing would likely try to appeal to Trump to get Cruz to back off.
This would be very valuable, because it would let Trump gauge how strong the opposition is, and who is behind it. If it is too strong, he could redirect Cruz to attack more vulnerable targets.