Does Ted Cruz have all the power?

[The Other Castro]

The more I think about it, it seems like Cruz may end up being the most powerful Republican in the primaries. He is the likely Iowa caucus winner, the emergency fallback break-in-case-of-Trump option, and a potential Trump VP. At any point in the race, he can effectively crown Trump the nominee by dropping out and endorsing him (for a VP position probably). More importantly, a brokered convention situation likely involves Trump, Cruz, and Rubio (or Christie). Trump obviously wouldn't achieve a majority as preventing his nomination is the reason for the brokered convention, but Rubio winning would require cooperation from Cruz. The most likely option here seems to be Rubio (at the behest of the RNC) frees his delegates for Cruz and makes him the nominee. Whatever happens, Cruz is likely either the kingmaker or the ultimate fallback.

[The Other Castro]

But what happens if Rubio does win? Cruz has zero fallback

It's not very clear at the moment how a Rubio victory would happen.

[The Other Castro]

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.

In that case, the Establishment can disqualify Cruz on grounds of not being a natural born citizen and still have Rubio as the nominee.

That's literally the worst possible thing they could do.