How low would Bitcoin have to fall before it was no longer recoverable?
Price, in my opinion, would not dictate this. It would have to be something that would destroy the foundation and system on which it is built.
what you say?
You could possibly imagine such scenario with altcoins, especially coins that are centralized like BNB, XRP etc. The project owners might decide to remove liquidity or authorities could go after them which might cause it to crash drastically. A similar example is LUNA that was worth $116 at some point, but crashed to many zeros and hasn't recovered.
I don't see such possibility with Bitcoin because it is completely uncensored. It is currently trading at $29.5k with the highest marketcap cap of 573.76 billion and it is not one of those shitcoins out there that would rise to a point and take a huge fall after a while. Anything that would make Bitcoin fall from whatever price to $1, that would not only be the end of Bitcoin but the end of cryptocurrency.