I can speak with some confidence as I browse almost exclusively without js. If a site needs it, I just move on [2].
Most sites still render a lot (sometimes revealing more) of their content perfectly without it.
As other HN commentators have noted, there's a strong negative correlation between sites that are js heavy and quality. Very little of value is lost by avoiding them.
[1] Too many because it seems a those that don't work without js also break legally required accessibility standards and are mainly from bigger entities who should behave better.
[2] About the only thing I can't seem to do on HN as a text-only reader is up/down vote other posters. That's also a feature.
As of how many... feels like 1 in 20.