Without Trump, the presidential race focus would be on Obamacare, economy, foreign policy, and (now) the Supreme Court. Even if Cruz were to have brought immigration/amnesty up as a topic, it wouldn’t be his cornerstone issue. Plus, because of the way Cruz has been selling himself in the race, he’d be seeking only the evangelist vote. Immigration would never be presented to the general electorate.
Without Trump, the media would have taken out Cruz early and we’d be running with a jeb/scRubio ticket while Hillary picked out Oval Office drapes and a new email server.