He might not reach 1237, but Cruz and Kasich won't get there either.
If Trump misses 1237 yet still finishes comfortably ahead of Cruz and Kasich, then you give the nomination to Trump nonetheless.
The only way you don't give it to Trump automatically is if Cruz or Kasich are close. But that won't happen. Cruz and Kasich will be distant a 2nd and 3rd.
The bottom line here is that Trump keeps winning. State after state. Right now, he's only losing Ohio, which is big, but he's losing to a popular Governor for whom the GOP Establishment rode to the rescue. He's projected to win IL and NC at this time, and he's leading Cruz in MO, although it's close. He's got 40% in every state he won, and 37% in the only state he lost.
How the GOP can ignore this and win in November is beyond me. I'm told Trump will bring the ticket down, but how is a convention whose sole purpose is to undercut Trump going to help the eventual Republican nominee? All of the scheming and plotting is going to happen on TV and internet streaming; it's not like 1924 when it was only radio, and that was limited. Trump CAN be denied, but only at a HIGH price, and it's a price lots of folks are skittish about paying.