Could not find “fall apart” or “falls apart” in a relevant context. Found a few “when it happens”. I don’t think any of them are what you’re looking for, but the second (from Part 3, Ch 2 ) is probably around the area that you should check again. Just for fun, here are the three quotes I found.
**** ATLAS SHRUGGED SPOILER ALERT ***
“When it happens”
Nobody came to get me, no destroyer, perhaps there never was any destroyer, after all. I don’t know what I’ll do next, but I have to get away, so that I won’t have to see any of them for a while. Then I’ll decide. I know that you can’t go with me right now."
“No. I have two weeks in which they expect me to sign their Gift Certificate. I want to be right here when the two weeks expire.”
“Do you need me—for the two weeks?”
“No. It’s worse for you than for me. You have no way to fight them. I have. I think I’m glad they did it. It’s clear and final. Don’t worry about me. Rest. Rest from all of it, first.”
“Yes.”
“Where are you going?”
“To the country. To a cabin I own in the Berkshires. If you want to see me, Eddie Willers will tell you the way to get there. I’ll be back in two weeks.”
“Will you do me a favor?”
“Yes.” <as_514>
“Don’t come back until I come for you.”
“But I want to be here, when it happens.”
“Leave that up to me.”
(Part 2, Ch VI, Miracle Metal)
“You’re not thinking of going back to that hell for another year, are you?” said Mulligan.
“I am.”
“But—good God, John!—what for?”
“I’ll tell you, when I’ve decided.”
“But there’s nothing left there for you to do. We got everybody we knew of or can hope to know of. Our list is completed, except for Hank Rearden—and we’ll get him before the year is over—and Miss Taggart, if she so chooses. That’s all. Your job is done. There’s nothing to look for, out there—except the final crash, when the roof comes down on their heads.”
“I know it.”
“John, yours is the one head I don’t want to be there when it happens.”
“You’ve never had to worry about me.”
(Part 3, Ch-II, Utopia of Greed)
“I …” She made an effort to breathe. “I see … Who are you?”
“The name wouldn’t matter. When I hang up, I will have become a deserter. I don’t want to stay here to see it when it happens. I don’t want any part of it any more. Good luck to you, Miss Taggart.” She heard the click. “Thank you,” she said over a dead wire.
(Part 3, Ch 5: Their Brothers Keeper)