For most subreddits it is temporary blackout but some communities like one of the piracy subreddits I saw completely packed bags and the mods moved to lemmy. It’s too early to say if reddit is over or if this is just a temporary setback. Reddit may even concede and revert some of their api changes to appease the populace. Simply put, we don’t know enough yet.

The blackout itself is an initiative by the community. However, from June 30th third party apps will no longer work, and many users (and moderators of many large subs) have explicitly said that they aren’t interested in continuing with the official Reddit app or site. This will cause a huge chunk of reddit users to leave. Some will go back, some won’t. Besides that, it’s a matter of principle. They’re choosing stakeholders over users.