By end 2028, at least 24 of the 30 videos in this list are not available on YouTube any longer based on the conditions below
This is the page "List of most-viewed YouTube videos" https://en.wikipedia.org/wiki/List_of_most-viewed_YouTube_videos as of 10/8/2023
To qualify as NO, at least 24 of these have to be:
available in the US
for free
is available without proving one's real identificaiton requirements beyond what would be required today (i.e. if today a video requires some kind of auth/validation, it requires that or less, and isn't more onerous in the future)
Alternative ways this could YES:
If YouTube is politically blocked in significant areas of the US (10%+ population)
YouTube is out of business
In general there is no internet anymore
If there is a large copyright strike wave, that could qualify this.
The unavailability has to persist for at least 30 days; this is to avoid a temporary blip for something like a legal problem, or a generalized national networking failure from disaster or attack. Those reasons can still lead to this being YES if they last >30 days, though. I will be testing this myself & via friends in various places.