A brokered convention is imminent. There's no way Trump will win enough states and Cruz will eventually fade just like Santorum in 2012. Rubio will emerge as the establishment candidate once Jeb & Christie drop out; at the convention Rubio will be chosen to be the nominee.
If Cruz fades then that would seem to guarantee a Trump win.
Trump doesn't have high enough favorabliity ratings to garner wins in larger states like California. If Cruz fades it leaves only Rubio left to take over and become a John Kerry. Trump will diffuse himself, just like Howard Dean in '04