Okay, but I fail to see how this eventuality results in the end of ads. Owners of websites, at least the popular ones, won't stop running ads just because they don't strictly need to. We've seen this play out repeatedly with companies pushing ads to paying subscribers who are not paying a small amount to access their services.
The other unfortunate outcome I immediately foresee is that by adding an element of risk to visiting a new site (of wasting money on something useless, even a tiny amount), people will be even more inclined to stay within walled gardens they already know rather than explore the internet. This takes a problem we already have and makes it way worse.