It’s not possible to survive behind a paywall because the next site provides similar content “for free”. I think it’s hard to say how the competitive landscape in e.g news would look if ad revenue was drastically cut online.

If ads don’t pay the next site’s bills either, then sites would have to compete for paywall customers with quality. Even if a large fraction of news sites died I don’t see a big problem since the quality of the remaining outlets would be higher, and prices lower as more customers choose among more paid services. Clickbait would almost completely be a thing of the past, if there as no revenue in ads, for example.