I bet a lot of the 'live' stuff is effectively dead, too: squatted, sold and repurposed domains. But that would be much harder to check for. Perhaps a "heat map" showing how many DNS changes the domain for each ad has undergone since 2005?
These non-functioning links account for 221,900 of the million pixels—$221,900 worth of real estate, assuming the pixels have kept their value in the last eight years.
The atrophy of links has been shown to stabilize over time, meaning we should expect fewer than 22% of links to break over the next eight years. The longer a link continues to work on a webpage, the longer it can been expected to work into the future.
Nonetheless, it remains a problem for thought experiments and seminal works alike. Researchers at Harvard found that at least 50% of URL-based legal citations in US Supreme Court opinions, for instance, no longer point to the originally referenced material.