If it was a website, maybe it can survive no matter what? But if they can get Google and Apple to take the app down in the US market, you effectively kill the app. I‘m sure some will sideload, but relatively speaking, it’ll be a small amt of people.
I haven’t checked the top sites in US list recently, but I imagine even for places that have sites on top of apps, losing App Store access will destroy a large part of the user base. Off the top of head, Google, the surviving portal sites, could survive. But even portal sites like Yahoo likely get enough traffic from apps that they’d be hit hard. Same with Reddit, Facebook, Pinterest. Maybe LinkedIn would go largely unscathed.