I feel this won't happen. If big subs continue to be dark too long, the reddit admins would simply remove the hostile volunteer mods and reopen the subs. The mods are used to being gods of their little domains. If they cross the line, they will be reminded that they own nothing. They can obey reddit or they can be replaced.
That is what I see in the future for any mods that try to hold subs hostage indefinitely.