Unless you can figure out how to throw out each and every single Republican in the House and Senate on their ass, whoever is president will have to make deals with the GOP. Even Cruz would have to do so. It seems likely he already has due to half of them endorsing him.
Whoever is president will have to get SCOTUS nominees confirmed, vetos sustained, cabinet picks confirmed, etc. Cruz can stand there as a solid concrete wall and prevent anything from being passed for maybe a year, and then Congress will start overriding his veto left and right. At that point we will probably turn into a parliamentary system with the Speaker of the House being head of government. That will be Ryan.
Bwahahahaha.