Most newspapers could make old-style ad deals, like they do for print. A few newspapers also still finance their sites almost entirely through subscriptions, and those would continue to exist (e.g. Süddeutsche, SPIEGEL). As would obviously publicly financed sites (BBC, ARD, ZDF, NPR).
Also products financed via paying customers, such as imgur used to be, or possibly reddit if they change the way reddit gold works.
Also, most people's blogs would continue to exist, as many self-host or use services where the free users are subsidized by the paying ones. Even WhatsApp used to be profitable with that model.
We'd be going back to a 2010 era web, and I'm not so sure that's actually bad. We'd lose the corporate dominance over the web, Google, Facebook, etc.
Now, there is one part where paying user subsidizing doesn't work, but where ads are currently the only model of financing, and that's search engines.
But considering those act as a public service, maybe after advertisers leave the web and Google goes down crashing, a government could just buy Google (as the German government bought DHL, or major shares in VW, they could probably just outright buy Google).