Does Ted Cruz have all the power?

[Why]

If there does end up being a three way split of the delegates and the establishment decides that it has to be anyone but Trump then Cruz will be the nominee even if he finishes 3rd.
If Cruz finishes 3rd Trump will offer him the VP. Rubio will offer him the VP. Cruz then says to Rubio, either back me for the nomination or I support Trump and become his VP. Rubio then has to accept to stop Trump becoming the nominee.
So a Cruz, Rubio ticket is the best the establishment can hope for from a brokered convention.

[Why]

But there is the what if scenario. What if Rubio does emerge? Cruz has zero chance.

If Rubio wins a majority of delegates, then, of course, Cruz has nothing but that seems less likely than a Trump win, or a Cruz win or a three way split of the delegates.

[Why]

Cruz doesn't have anything until he actually wins Iowa. There is an outside chance that Trump could win it, in which case it's all over for everybody.

Of course that is true. Not winning Iowa would be disastrous especially if he is built up as the favorite in the week prior to the vote.