600 post views per day qualifies pretty close to "irrecoverably down" for me.
That's an odd definition of irrecoverable you have there.
> It's already normal for people to have both a Twitter and an Instagram account.
This is the key! Because now if Twitter or Elon annoys you, you just delete Twitter and are already on an identical service with all your followers essentially.
Sure, the fediverse has been growing, but most users haven't left Twitter, they've just also made an account on the fediverse. I don't see how this will be any different. It's already normal for people to have both a Twitter and an Instagram account, or even stuff like both a TikTok account and posting shorts on YouTube.