In a comment shared by r/Apple moderator @aaronp613, Reddit cited its Moderator Code of Conduct and said that it has a duty to keep communities “relied upon by thousands or even millions of users” operational. Mods who do not agree to reopen subreddits that have gone private will be removed.
If a moderator team unanimously decides to stop moderating, we will invite new, active moderators to keep these spaces open and accessible to users. If there is no consensus, but at least one mod wants to keep the community going, we will respect their decisions and remove those who no longer want to moderate from the mod team.
They can’t be replaced in this case - unless Reddit wants to spend lots of $$$ hiring moderators. As long as they leave that power to community mods, it is impossible for them to stop this type of protest.
I do think there is a real possibility Reddit will consider this a long-term risk and replace them with paid mods.