He has to keep up the cascade that Cruz can be nominated at the convention so those opposing Trump will continue to for Cruz. As soon as Trump cannot get the delegates officially then Cruz is toast and the RNC will go through the motions of “having” to approve a compromise candidate in Ryan, Romney, Bush, etc.
Watch the video I posted in 39, Reince unequivocally states the nominee has to be someone currently running and who has won at least eight states.