If ad-based business models truly become unviable, they will find a new one. Ad-based businesses suck all the air out of the room, preventing other models from even forming. It'll take effort to find better models, but they'll come. But TBH, I don't see the ad-based model dying any time soon.
There are plenty of reasons to post good content that are not related to ads, and very weird incentives to write good content otherwise. Content for ads is riddled with SEO, hyped headlines, short shallow and unoriginal articles.
Good content is posted by people and companies for indirect benefits: a researcher makes videos about papers to motivate and held himself accountable to the public, a company publishes documentation and tutorials that are related to their business, a hobbyist does the same for pure fun. A teacher posts lesson plans to collaborate with other teachers. We'll be fine without content-for-ads.
