If humans don’t click through and visit the websites from where the content was accessed for free by the engines, then the websites will eventually all die. A minuscule number of them may survive behind paywalls. Where will the engines go in future for new content?

We're already seeing a lot of that even without the death of the ad model.
I'm already sick of going to web sites, even from reputable knowledgeable companies, and finding little other than AI slop as content. As for a page about, say, tire compounds, and the first 200 words are a paragraph about "What is a tire?", and the last 200 under the "In Conclusion" section, it concludes you should buy tires.

Perhaps the LLM crawlers can discount a lot of that rather than get a crap feedback death loop--maybe--but the broader death of "ordinary" content web sites is accelerating for more than one reason.

I used to mock those "enthusiast" pages with black backgrounds and 12 colours of blinking text and italics, and a page hit counter at the bottom, but now I miss them. They were written by humans who cared, some fraction of whom were actually knowledgeable.

Jim