Can they, or will they be delisted if they do that?

From the Patreon FAQ:

> Can I opt out of the App Store Fee?

> For U.S. fans, there’s still a way to avoid Apple’s fee. When signing up in the iOS app, they can choose web checkout instead of Apple’s in-app purchase system. Apple’s rules require that any paid content shown in the iOS app is also available to purchase through Apple’s in-app system.

https://support.patreon.com/hc/en-us/articles/28801582599181...