People who use third party apps are outliers. They do not make Reddit any money so Reddit would be glad to be rid of them while also saving on API costs. No other online service allows freeloading millions upon millions of API requests in addition to allowing third party apps to a large extent. Facebook, Whatsapp, Discord, Instagram, Slack, Twitter all don't, so it's a wonder that Reddit did all this time, for free.
If subreddits go dark for 48 hours, then from the perspective of Reddit, they'd think, great, then it returns to normal. If they go dark indefinitely, Reddit admins will wait a few days then force the subs open and demod everyone involved. There is a long list of mods who are willing to contribute.
In the end, consumer boycotts like this simply don't work.